Which one? A comparative study of traditional and sports uniforms on academic achievement, cognitive performance, playtime, bullying, and discrimination in adolescents. The Cogni-Action Project

<jats:title>Abstract</jats:title>         <jats:p>Objective  The aim of the study was to compare academic achievement, cognitive performance, playtime, bullying, and discrimination in adolescents according to traditional (TU) and sports uniforms (SU) worn at school, while simultaneously exploring the influence of the school vulnerability index. Methods  Nine hundred eighty-eight Chilean adolescents (52.6% boys) aged 10–14 years participated in this cross-sectional study. Academic achievement was evaluated by the average grade in maths, language, and science grades, while the cognitive performance was assessed through eight cognitive tasks. TU affecting physical activity, playtime, bullying, and discrimination were queried. Mixed model analyses were performed. Results  No differences were observed in academic achievement (TU: 5.4 ± 0.1 vs. SU: 5.5 ± 0.2, p-value = 0.785) or in cognitive performance (TU: 99.6 ± 0.8 vs. SU: 98.9 ± 1.8, p-value = 0.754) according to school uniform type. Moreover, 64.1% of participants declared that wearing TU affects their physical activity, and those who believed so spent more time playing than those who answered negatively (14.5 min, p-value = 0.012). Finally, adolescents wearing SU displayed a lower feeling of bullying and discrimination; this finding depended mainly on the school’s vulnerability. Conclusion  It is concluded that wearing a TU does not show an educational advantage at an academic and cognitive level that justifies its obligation. In addition, it could be suggested that schools consider adolescents’ opinions in adopting a more comfortable uniform, such as the SU. This feasible and low-cost measure would help to increase adolescents' physical activity during the school day and, contrary to belief, it would not be related to increased feelings of bullying and discrimination.</jats:p>

section_content: School uniforms have an important social context; in fact, in New Zealand, it is a reason why students choose their schools 1, but in general, uniforms have been adopted as strategies by principals and governments to improve educational test scores and student behaviour 2, 3. Indeed, several studies have suggested that traditional uniforms remove social differences, increase security, reduce violence, improve school climate and discipline, promote social responsibility, and improve academic achievement 2, [4] [5] [6] [7] [8]. 

However, ndings on this matter are highly sparse and heterogeneous and seem to be dependent on the population studied, age, race, educational context, and socioeconomic status 2, 3, 6, 9, 10, and of the aforementioned features have not been proven yet 3, 6, 7. 

Due to COVID-19, many schools have performed their classes virtually, and uniforms have not been mandatory. Moreover, this global health concern has been generating economic harm at the social and family levels 11 ; thus, many schools and families have begun to question its use. Overall, school uniforms limit self-expression, are expensive, and most schools require that families buy several uniforms (i. e., for winter, summer, sports, formal occasions) even from speci c shops 8, 12, 13. Furthermore, in some countries like Chile, not wearing a traditional uniform has been used as a reason for school expulsion, contravening current national regulations 14. 

A recent review has identi ed three main topics related to wearing school uniforms (i. e., impact on academic achievement, physical, and psychological health) 6, all of which are relevant for generating social and educational policy, especially in vulnerable communities 6. In this sense, Latin-American schools share certain features (i. e., economic, social, and cultural status) that seem to be stronger predictors of adolescents' academic and cognitive performance than family socioeconomic status 15. Indeed, a study in Chilean adolescents showed that a potent socioeconomic indicator at school level (i. e., the school vulnerability index [SVI]) was negatively related to physical tness and cognitive performance 16. Moreover, economic, social, and cultural status related to the school climate 17, which in turn promoted greater learning and reduced bullying and con icts among students 18. To date, there is a lack of studies exploring differences between types of uniforms and their effect on academic, cognitive, physical activity, and psychological indicators such as bullying and discrimination feelings in the same student sample. 

Therefore, this study was divided into three objectives. First, to determine whether adolescents wearing traditional uniforms present higher educational achievements (i. e., academic achievement and cognitive performance) than if they were wearing sports uniforms. Second, playtime according to the uniform type was explored regarding whether traditional uniforms affect adolescents' physical activity. Third, to compare feelings of bullying and discrimination at school according to the uniform worn. Finally, based on the relevance of socioeconomic factors, it was hypothesised that possible differences between groups depend mainly on the SVI (a proxy of socioeconomic indicators at school level) rather than the uniform type.
section_name: Introduction

section_name: Methods

section_content: This cross-sectional study is part of the Cogni-Action Project carried out from March 2017 to October 2019 19. The project was conducted according to the guidelines of the Declaration of Helsinki and approved by the Bioethics and Biosafety Committee of the Ethics Committee of Ponti cia Universidad Católica de Valparaíso (BIOEPUCV-H103-2016). Written consents were obtained before participation from the school principal, parents, and participants.
section_name: Study design and ethical requirements

section_content: A total of 1,296 adolescents, between the ages of 10 and 14, from 19 public, subsidised (i. e., schools that receive partially governmental and private economic support), and private schools of the Valparaiso region (Chile) participated in this study. From the 1,296 participants, a total of 308 adolescents were removed because their school (k = 4) wore a mixture of uniforms (a detailed explanation in the next section). Thus, a total of 988 adolescents participated in this study from 15 schools (k = 12 schools wearing traditional uniforms and k = 3 schools wearing sports uniforms).
section_name: Participants

section_content: Traditional uniforms: schools that declare their students wear a traditional uniform all weekdays except for physical education classes in which adolescents wear sports uniforms. A traditional uniform for male adolescents was outlined as a polo shirt or shirt (with school necktie), sweater or blazer and trousers, and for girls, a skirt and blouse, and sweater or blazer, both with school shoes (usually black leather). 

Sports uniforms: schools that declare their students wear sports uniforms every day. A sports uniform consisted of adolescents (both boys and girls) wearing mainly sportswear such as polo shirts or t-shirts and sport or short trousers (jeans were included as well in this category due to their generalised wearing), and sneakers. 

Mix uniforms: Four schools were excluded due to adolescents wearing traditional uniforms most days but sports uniforms during the day when they have physical education classes. 

Educational achievements: Academic achievement and cognitive performance Academic achievement was established by asking students their general average of the last semester in language, mathematics, and science and were averaged. Grades in Chile are scored between 1 (minimum) and 7 (maximum) in which a grade of 4 implies approval. These three subjects are part of the Programme for International Student Assessment. 

The adolescents' cognitive performance was evaluated through eight neurocognitive tasks from the NeuroCognitive Performance Test (NCPT) from Lumos Labs, Inc 20. This battery included: "Trail Making A and B" assessing attention, cognitive exibility, and processing speed; the "Forward Memory Span" and the "Reverse Memory Span" evaluating short-term visual memory and working memory; the "Go/No-Go" test, assessing inhibitory control and processing speed; the "Balance Scale," indicating quantitative and analogical reasoning; the "Digit Symbol Coding," valuing processing speed; and nally, the "Progressive Matrices," assessing problem-solving and reasoning/intelligence 20. Each test was scaled following a normal inverse transformation of the percentile rank and summed 21 obtaining a global cognitive score.
section_name: School uniform type

section_content: Playtime was estimated by the Chilean physical activity questionnaire validated in the population aged 8-13 years-old 22. Adolescents were asked about several physical activities. For this study, only a playtime item was considered. This item asks about daily play (hours and min) in activities such as riding a bicycle, ball games, running, etc.
section_name: Playtime

section_content: Adolescents were asked about the daily in uence of traditional uniforms on physical activity levels. They respond ''yes'' or ''no'' to the following question: Do you think that wearing a traditional uniform in school affects your physical activity? The interviewers explained that the question refers to a decrease in the levels of physical activity during the school day.
section_name: Perception of traditional uniforms affecting physical activity

section_content: Based on the questionnaire "Validation of a daily stress scale in Chilean schoolchildren" 23, we extract two questions: 1) Have you suffered bullying in the classroom or in the schoolyard? and 2) Have you suffered discrimination in the classroom or the school playground? 23. Each question scores from 1 to 4 concerning the frequency of the event (never: 1, sometimes: 2, usually: 3, and always: 4).
section_name: Suffered bullying and discrimination

section_content: Six covariates (age, sex, maturation, physical tness, BMI, and SVI) were included in the analyses because of relevance and relationship with outcomes. It has been stated that sex and maturation are relevant factors associated with behaviours, cognitive, and brain development 24. The maturation was calculated according to the peak height velocity (PHV), subtracting the PHV age from the chronological age. Differences among years were established as maturity offset value 25. 

Physical tness was evaluated by the ALPHA-tness test battery 26, which comprises the assessment of cardiorespiratory tness, muscular tness, and speed-agility tness. A z-score of each component was calculated adjusted for age and sex, and all three were added. Procedures and methodological details were published previously 21. 

The height and weight were measured with a digital scale OMRON (HN-289-LA, Kyoto, Japan) with a precision of 0. 1 kg and a portable stadiometer SECA (model 213, GmbH, Germany) with a precision of 0. 1 cm, respectively. The World Health Organisation 2007 growth reference was used to determine the body mass index expressed in z-score (BMI Z ) for school-age children 27. 

Additionally, SVI was included as a proxy of a socioeconomic factor at school level (model 2). This Chilean index measures the degree of socioeconomic vulnerability of pupils who attend schools with partial or total state funding (subsidised and public schools, respectively) based on the educational level of parents-tutors, student health condition, physical and emotional wellbeing, and school location. This index score ranges from 0 to 100, a score of zero being assigned to the private schools, thus schools were classi ed as low (< 10), middle (≥ 10 to < 60), and high (≥ 60) 28.
section_name: Covariates

section_content: Before analyses, data were imputed based on a non-parametric missing value method using random forest through the "missForest" R package 29. This function successfully imputes large and complex mixed-type datasets (quantitative and/or categorical variables), including complex interactions and nonlinear relations by a random forest trained on the observed values predicting the missing values. Missing data ranges were between 1. 0-27. 0% and estimation error was 0. 081 (numeric variables) and 0. 082 (factor variables). The central limit theorem for sample sizes over 500 participants was considered 30. A Q-Q plot (quantile-quantile plot) was used for checking normality visually. Additionally, we explore a possible interaction by sex and age. No interaction was observed; thus, analyses were not strati ed by sex or age. Differences between groups were tested (t-test or chi-square according to variable features). 

Mixed model analyses were performed to establish differences between traditional and sports uniforms at the academic and cognitive performance, between those who respond that traditional uniforms affect their physical activity level (yes/no) at playtime, and nally at bullying and discrimination feelings. To compare the likelihood of a model with the effect included versus a model with the effect excluded, the likelihood-ratio test (LTR) for the random effect was estimated. A signi cant value indicates that the model with random effect is signi cantly better (in terms of likelihood) than the model without the cluster. Post-hoc tests were estimated using the Holm correction to multiple comparisons. For all analyses, signi cant values were established at p < 0. 05. All models were adjusted for multiple covariates. Model 1 included sex, PHV, BMIz, and physical tness, while model 2 added the SVI in order to test the study hypothesis. Adolescent schools (k = 15) were used as clusters (random effect). All statistical analyses were conducted using the General, Mixed and Generalised Models module by Gallucci (2019) 31. We present plots to simplify the main ndings; however, complete tables with both models are presented as supplementary material. Proportion test (2 outcomes) was used to establish differences in frequency response (yes/no) to the question: "Do you think that wearing a traditional uniform in school affects your physical activity?". Moreover, contingency tables and X 2 tests were carried out to describe and corroborate, respectively, differences between answer categories for bullying and discrimination. All analyses were performed using the statistical software Jamovi version 2. 0. 0. 0 (The Jamovi Project) 32.
section_name: Statistical analysis

section_content: Table 1 shows the descriptive characteristics of the sample. In this study, a total of 988 adolescents participated, of them, 854 (86. 4%) wore a traditional uniform (k = 12 schools) and 134 (13. 6%) wore a sports uniform (k = 3 schools). Schools where adolescents wear traditional uniforms were public (k = 7), subsidised (k = 4), and private (k = 1), and nine presented high-SVI, two middle-SVI, and one low-SVI, while schools where adolescents wear sports uniforms were subsidised (k = 2) and private (k = 1), and two presented middle-SVI and one low-SVI. Data are presented as mean ± SD or frequency (%) according to variable features. P-value: signi cant differences between groups (t-test or chi-square according to variable features). 

Figure 1A shows no signi cant differences between uniform types in academic achievement (random effect LTR was 44. 0; p-value <0. 001). Figure 1B displays no signi cant differences between uniform types in cognitive performance (random effect LTR was 21. 7; p-value <0. 001). Consistent results were found using model 1 and model 2 in both analyses (see supplementary material). 

For the question, "Do you think that wearing a traditional uniform in school affects your physical activity?", 64. 1% of adolescents believe that the traditional uniform affects it (proportion test, p < 0. 01). 

Those that responded a rmatively play 14. 5 min more than those who respond negatively (p = 0. 012). 

Moreover, considering only those who responded a rmatively showed higher playtime than those who responded negatively (traditional uniforms: +8 min and sports uniforms: +20 min, both p > 0. 05, and random effect LTR was 0. 11; p-value = 0. 739). Consistent results were found using model 1 and model 2 (see supplementary material). 

Figure 3A shows no signi cant differences between uniform types in feeling of bullying (random effect LTR was 8. 20; p-value < 0. 01; see supplementary material). Consistent results were found using model 1 and model 2, but there is a trend in model 1 (p = 0. 064). While Fig. 3B displays no signi cant discrimination differences between groups in model 2 (random effect LTR was 7. 60; p-value < 0. 01), a higher discrimination feeling was found in adolescents wearing traditional uniforms in model 1 (traditional uniforms: 1. 41 ± 0. 05 vs. sports uniforms: 1. 13 ± 0. 11, p-value = 0. 041). The random effect LTR was 23. 76; p-value < 0. 01. 

Tables 2 and 3 show the proportion of responses with regard to bullying and discrimination feelings of adolescents wearing traditional or sports uniforms. Signi cant differences in answer frequency according to bullying and discrimination feelings (X 2 = 10. 7; p = 0. 012 and X 2 = 10. 3; p < 0. 001, respectively). Lower answer frequency is observed in "usually" and "always" categories in schools wearing sports uniforms, both bullying and discrimination.
section_name: Results

section_content: Differences in academic achievement and cognitive performance

The rst aim was to establish whether adolescents who wear traditional uniforms present higher academic and cognitive performance than those who wear sports uniforms. The present ndings did not nd any signi cant differences in both educational outcomes. 

In line with our ndings, a Korean study that explored the link between uniforms and appearance restrictions in middle schools and high schools found no evidence that wearing school uniforms leads to better academic achievement and reported that uniforms would deny the expression of individuality and creativity 33. Concerning creativity, it is an essential cognitive resource that is fundamental in the learning processes. In this line, a meta-analysis including 120 studies concludes a signi cantly stronger relationship between creativity and academic achievement 34 ; thus, traditional uniform wearing could in uence both cognitive skills and, in turn, academic achievement. Nonetheless, wearing traditional uniforms also could improve children's discipline, which was associated with a higher academic performance 35. 

To our knowledge, this is the rst study in a sample of Latin-American adolescents exploring both educational outcomes and type of uniform, and the lack of studies related to this topic makes the comparison di cult. Therefore, the present ndings contribute to clarifying the scarce and divergent evidence on this matter. 6 They also demonstrate that, independently of relevant covariates related to academic and cognitive performance, such as physical tness, body composition, maturation, and school vulnerability, wearing a traditional uniform was not related to educational outcomes.
section_name: Discussion

section_content: The second aim was to ask adolescents whether wearing a traditional uniform affects their physical activity, and their answers were compared to playtime according to the type of uniform. Two relevant ndings were observed; rst, 64. 1% of adolescents declared that traditional uniforms affect their physical activity negatively. The second, those who responded a rmatively played 14. 5 min more than those who responded negatively. Likewise, a difference of 20 min of playtime was detected in adolescents who responded positively to the question and wore sports uniforms (without statistical signi cance but ). 

In line with the rst nding, a study in an Australian primary school found similar results, where 62% of schoolchildren preferred to wear their sports uniform every day and believe they would be more active if they could do so 36. Moreover, a study in public middle school students found that 87. 3% of them dislike wearing a traditional uniform 2. Hence, the present nding from a Latin-American country con rms the opinion of Australian 36 and United States 2 students contributing to the literature gap in this matter. 

Regarding the second nding, the present study highlights two main results, one with a statistical signi cance (playtime: 14. 5 min) and the other without (playtime: 20 min). This has a justi cation at the public health level relevant to discuss. On the one hand, a study reported signi cant differences in girls' physical activity levels over boys during breaks and lunch when they wore a sports uniform 37. In this line, girls declare that wearing traditional uniforms limits performing physical activities during school time 38. These two studies support our ndings, but we do not nd differences at the sex level, which suggests that both girls and boys in this group of Chilean adolescents could bene t from wearing sports uniforms. 

On the other hand, adolescents who believe that the traditional uniforms affect their physical activity played 20 min more than those who do not believe so. This non-signi cant statistical difference could account for a third of the daily physical activity recommendation for children and adolescents 39. 

Although many physical activity interventions in schools have shown modest effects 40, small modi cations are signi cant for getting health bene ts in real contexts 39, 40. 

Important to highlight is that schools' principals seem to be a key barrier related to attitudes to changing school uniform policies allowing students to wear sports uniforms every day, but not teachers, parents, and students 36. The central concern is that the sports uniform does not t with ceremonial and formal activities at school. Indeed, in Chile, the school uniform must be agreed upon by principals, teachers, parents and students 5 ; however, the traditional uniform is widely worn. Thus, institutional measures supported by government policies are essential to creating the conditions at the interpersonal level to promote behavioural changes in adolescents. 

Therefore, the present ndings contribute to the literature showing that promoting a comfortable school uniform could help to increase physical activity in adolescents. Interventional approaches are necessary to corroborate this assumption. Moreover, these ndings are useful for future internal school regulations, as well as public policies at educational and health levels due to the prevalence of obesity, physical inactivity, low tness performance, and educational achievement observed especially in schoolchildren from developing countries [41] [42] [43] [44]. 

Bullying and discrimination feelings third aim was to compare bullying and discrimination feelings at school according to adolescents' uniform type. In this sense, the present ndings seem contrary to social belief and some studies in this matter 2, 6, showing similar feelings between groups in both indicators when the model is adjusted for SVI (model 2). 

Bullying and discrimination are a global concern at the educational level. For instance, in Chile, 62% of students have reported having been victims of bullying. This percentage is one of the highest percentages based on countries assessed by the Trends in International Mathematics and Science Study - 2011 45. One central reason is that Chile has one of the highest levels of inequality in Latin America, and its educational system has generated a high level of social segregation among the various types of schools 46, 47. These economic and social fundamentals have been associated with a greater prevalence of bullying and, in turn, being a bully victim has been negatively correlated with academic and cognitive performance 46. However, we cannot establish causality considering bullying as the base of lower educational achievement because there is also the possibility that students who have lower performance choose to bully others 46. 

In addition, a U. S. study including 6,320 children from a nationally representative sample who were followed from kindergarten entry through the end of fth grade found that those who wore uniforms did not demonstrate better social behaviour (i. e., social skills, internalising, and externalising behaviour) 48. Relevant to note is that their ndings were even across both public and private schools. Moreover, another study that compared students' opinions (n = 604) on the bene ts of wearing a school uniform after implementing this measure in a public school in Nevada found a potential effect to improve the school climate and students' experiences. However, students' beliefs did not support these changes 2. In the case of a low-middle-income country (i. e., Mongolia) has reported schoolchildren exclusion feelings when most students wear uniforms in school 49. 

Finally, and connecting this result with the previous nding addressed, the early detection of bullying and discrimination is fundamental as it could strengthen the social relationships among students and improve school coexistence, where physical activity plays a vital role at school 50. Furthermore, increased physical activity has been associated with reduced bullying victimization, enhanced cognitive performance and academic achievement 21, 51, 52. Therefore, in this large sample of Chilean adolescents, the kind of uniform wore was not related to bullying and discrimination, solving great social, family, and school principals' concerns. 

In uence of school vulnerability Finally, was hypothesised that possible differences in our analyses would depend mainly on the school vulnerability than the uniform type. This assumption was based on the importance and convergence of factors such as socioeconomics, inequality, and the vulnerability index at the school levels in a Latin-American sample of adolescents 16, 28, 53. Contrary to our hypothesis, model 1 and model 2 seem to be consistent and not affected by the school's vulnerability in academic achievement, cognitive performance, playtime, and bullying. 

Nonetheless, discrimination was signi cantly affected when SVI was not present in the analysis (model 1). In other words, discrimination appreciated by students at schools seems to depend mainly on the social and economic features of the educational establishment and not on the uniform worn. In line with this nding, a study addressing the perceptions of school uniforms with socioeconomic statuses established that students of diverse socioeconomic statuses perceive school uniforms similarly 10. In addition, a multilevel study of school violence in 52 countries concluded that income inequality was the main determinant of school violence 46. Thereby, future education policies oriented to reduce bullying and discrimination might focus primarily on decreasing social gaps inside and outside the school, and in the speci c case of Chile, adolescents' school uniform seems to be not a particular determinant of bullying and discrimination.
section_name: perception and differences in playtime

section_content: Some strengths of this study were the large adolescent sample from a usually underrepresented region in this research area and the set of variables included (academic achievement, cognitive performance, playtime, bullying, and discrimination) that contribute to resolving a complex educational topic worldwide. Also, the cognitive performance score based on eight tasks strengthened the study measure. 

Furthermore, the present statistical analysis permitted control of the effect by cluster and explored a powerful indicator of school vulnerability. Finally, a large group of researchers living in Chile participated and reviewed this study. Some study limitations were the scarce evidence comparing traditional and sports uniforms and the nonassumption of causality due to the data characteristics. Playtime was evaluated by a self-reported question and not by objective measurement (i. e., accelerometers). Despite the large sample size of adolescents, it is not representative of Chile; hence extrapolations should be made with caution. Finally, the number of schools in each group (traditional or sports uniforms) was different, and schools where adolescents wear sports uniforms do not include any public establishment. In this sense, it is relevant to mention that school type (i. e., administration) has been associated with academic achievements, which could -to a certain extent --favour schools wearing sports uniforms. In this study, SVI shares variance with the school administration (r = 0. 480; p < 0. 01), nonetheless SVI is a potent indicator that includes not only the school administration but also other relevant indicators (detailed description in covariates, methods section), being highly related to several variables used in this study 16, 28, 53
section_name: Strength and limitations

section_content: Based on the present ndings and scholarly Chilean context, wearing a traditional uniform seems to have no crucial educational advantage at an academic and cognitive level compared to sports uniforms. 

Therefore, it could be recommended that the school community consider adolescents' opinions and increase instances for promoting a uniform that will be more comfortable such as sports uniforms, which could permit them to increase their physical activity during the school day. Additionally, this feasible and low-cost measure would not be related to higher feelings of bullying and discrimination.
section_name: Conclusion

section_content: Author Contributions: CC-M conceived and designed the data analysis and manuscript. CC-M was responsible for coordinating the study, acquiring the data, and writing the rst manuscript version. All authors contributed signi cantly to editing the manuscript and agreed to the nal version.
section_name: Declarations

section_name: Acknowledgement

section_content: We thank school principals, parents, and adolescents who supported this project. Carlos Cristi-Montero received funding for the Cogni-Action Project from the National Commission for Scienti c and Technological Research CONICYT/FONDECYT INICIACION 2016 grant No. 11160703 (Chile).
section_name: Acknowledgement

section_content: The authors declare that they have no competing interests.
section_name: Con icts of Interest:

section_name: Data Availability Statement:

section_content: The data presented in study are available on request from the corresponding author. The data are not publicly available as we did not obtain consent for public release of data.
section_name: Data Availability Statement:

section_name: Supplementary Files

section_content: This is a list of supplementary les associated with this preprint. Click to download.
section_name: Supplementary Files

section_name: Supplementarymaterial.docx