_Notes:_ All regressions control for pre-treatment outcomes, demographic controls (including dummies for age, gender, academic year, and ethnicity), and municipality fixed effects. Robust standard errors are clustered at the school level in parentheses. All figures are rounded to three decimal places. _Source:_ Own survey data, school year 2015/2016, own calculations.

Column 2 of Table 3 shows the average effect of the respective experimental condition on grit, which is our main outcome of interest. The finding is surprising and goes in the opposite direction of the hypothesized effect: it seems as if the intervention actually reduced students’ self-reported grit, particularly in case of student self-learning (by about 5% SD).

Grit is measured using the Short Grit Scale (Duckworth and Quinn, 2009), which is a standard instrument commonly used in the literature. The eight items in the scale set out to capture the two facets of grit: perseverance of effort and consistency of interest.

When looking at these two facets of grit separately (Table 3 Columns 3 and 4), we see an interesting pattern: while the intervention increased the perseverance-of-effort facet of grit (in both treatment arms, with again slightly stronger effects in the teacher-delivery treatment, about +6% SD _versus_ +5% SD), it reduced the consistency-of-interest facet (again in both treatment arms, by about -10% SD or more). Compared to students in the control group, treated students report being more industrious and hard-working but also report losing interest more quickly. Both facets combined then yield an insignificant (teacher-delivery) or even negative impact of the intervention (student self-learning treatment) on grit.

The divergence between the two facets of grit is puzzling. There could be several reasons behind this finding. First, some aspects of the Short Grit Scale may be less suited to the age group target of the intervention (that is, the Short Grit Scale being used in a younger cohort than it was originally developed for). For example, the concept of ‘projects’ may not be much applicable to the daily realities of sixth and seventh-grade students (who are between twelve and thirteen years old). Second, there may be a potential language translation problem, either in general or with respect to specific terms being used. For example, the term ‘projects’ has more than one meaning in Macedonian. Third, there may be a problem with reverse-coded items: the consistency-of-interest facet of grit is entirely captured by items that are reversely coded while the consistency-of-effort facet is not. It may be that, in the given country or target group, respondents might misinterpret how to answer these items.<sup>22</sup> When looking at the correlation between grit-effort and grit-interest in the pre-treatment period, we find only a weak (yet significant) correlation on average and for both Macedonian and Albanian language versions of the Short Grit Scale (+0.055 on average, +0.114 for Macedonian students, and -0.121 for Albanian students, all significant at the 1% level). Typically, the two facets of grit have been found to be more strongly correlated (although we similarly found a rather weak, negative correlation, i.e. -0.135, significant at the 5% level, in a large sample of Latin-American respondents).<sup>23</sup> So, while there may be some issues with the Short Grit Scale, these issues do not seem to be unique to our country context. Importantly, though, such issues by themselves do not necessarily explain why our intervention significantly _decreased_ grit-interest for treated

> 22 We cannot conclusively dispel the role of these factors. However, when translating the Short Grit Scale into Macedonian or Albanian language, we applied back and forth translation to make sure that there are no language translation problems (either in general or with respect to specific terms). Moreover, the Short Grit Scale (and all other instruments) was piloted in the country and with a random set of students in the targeted age group. The pilots also included qualitative discussions where none of the issues above came up. This gives us confidence in the correct application of the scale.

> 23 We used the 2017 round of the Development Bank for Latin America (CAF) annual household survey of sociodemographic information (N=10,687), which is representative of the adult population of major cities in Latin America. The 2017 round added the Short Grit Scale to the questionnaire (CAF, 2017).

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