Krølner et al. BMC Public Health 2012, 12:191 http://www.biomedcentral.com/1471-2458/12/191 conversation. Schools accepting to participate were asked to sign a written contract disregarding the result of the randomisation. In one of the included municipalities a school refused to participate due to involvement in too many projects and was replaced by a new school from the list. To ensure sufficient exposure contrast, one of the sampled municipalities in which schools already had a free FV programme, was excluded. A random sample of schools from the next municipality on the list of ran- domly selected municipalities was approached and all schools contacted in this municipality accepted to participate. On receipt of a signed contract on participation from all four schools within each municipality, schools were randomly allocated into intervention-and control groups by lot. All school classes of year 7 were asked to partici- pate. School classes of children with special needs were excluded from the evaluation study due to the complexity of the questionnaire. Effect-evaluation Questionnaires All Boost questionnaires were based on the validated Pro Children questionnaires for pupils, parents and staff, sup- plemented with items from other studies (e.g. The HBSC study, the HEIA study, North Carolina Child Health Assessment and Monitoring Program Survey (CHAMP) either transferred without any revision or adapted to the Boost study [56,76-79]. We also developed new items spe- cifically related to the Boost study. The pupil baseline questionnaire was tested among year 7 pupils (3 girls and 3 boys) to test time range for answering, followed by a focus group interview about comprehensiveness, layout etc. The questionnaire was changed accordingly. Ques- tionnaires for parents, principals and representatives were pretested among colleagues and friends, prioritising par- ents of year 7 pupils. Table 4 summarises the key mea- sures included in the Boost surveys matching the programme theory (Figure 1). Measures The primary outcomes measures were corresponding to the distal outcomes in the programme theory and mea- sured by two pupil-reported measures at all three time points: Total fruit-, vegetable-and FV intake in grams per day (in school + outside school) measured by the validated Pro Children pre-coded 24-hour recall questionnaire [77]. The 24-hour recall questionnaire measured how many pieces or portions of specific types of FV the pupils had con- sumed in five different time intervals on the previous day: before school, at school, after school, at dinner and after dinner. Pieces and portions of FV were converted into grams based on food weights applied by experts in the field [77,80]. The vegetable measure excluded potatoes. Page 13 of 25 The fruit measure included 100% natural juice but juice was only counted as one portion/100 grams a day regard- less of the number of glasses consumed. Pre-specified success indicator: Based on the effect size obtained in the Pro Children study [21], we aimed at a 20% increase in FV intake at intervention schools at 1st follow-up versus base- line and control school. This increase should be main- tained into 2nd follow-up. Habitual fruit-, vegetable-, and FV intake was measured by the validated Pro Children food frequency question- naire (FFQ) [77]. Fruit intake was measured by one item on fresh fruit. Vegetable intake was measured by three separate items: salad or grated vegetables, other raw vege- tables, and cooked vegetables. Pre-specified success indi- cator: Significantly higher proportions of pupils eating FV daily at intervention schools at 1st follow-up. This increase should be maintained into 2nd follow-up. Secondary outcomes were measured at all three time points and included 1) targeted determinants, correspond- ing to the proximal outcomes in the programme theory such as taste preferences, availability, and perceived paren- tal barriers for serving FV at home and explorative out- comes, corresponding to intended and unintended side- effects such as wellbeing and eating-related teasing, Proximal outcomes of the intervention: Changes in determinants Environmental, social and personal determinants were measured by questionnaires to pupils, parents, principals and representatives from sports-and youth clubs. The intervention programme was designed to create signifi- cant, positive changes in specific determinants of teen- agers’ FV consumption at intervention schools at 1st follow-up versus baseline and control schools. As shown in Table 4 the Boost study is characterised by thorough measures of both perceived and actual social and environ- mental influences (e.g. parental intake and home availabil- ity) using different data sources. We also measured potential confounders of the association between interven- tion and FV intake (determinants of FV intake which the intervention was not tailored to) such as school nutritional policies, family meal habits, family structure, and ethnic background (not shown in Table 4). Parental SEP (mod- erator in Figure 1) will be based on questions to parents and pupils on each parent’s educational and occupational background. Predefined explorative secondary outcomes: changes in positive and negative intended and unintended side-effects: Intended positive side effects and unintended adverse effects will be measured by questionnaires to the pupils and parents. We will assess whether there are significant changes in these among pupils at intervention schools ver- sus baseline and control group. Intended positive side-effects: At follow-up, the increased access to FV at intervention schools was