Krølner et al. BMC Public Health 2012, 12:191 http://www.biomedcentral.com/1471-2458/12/191 demonstrate corporate social responsibility and strengthen company image. We outlined the logistics necessitated by the project e.g. frequency of delivery and storage issues. The cooperative owner was responsible for recruiting the local FV providers for all intervention schools. Adoption among teachers and parents The one-day teacher workshop and the parent meeting intended to engage teachers and parents in the interven- tion. Local coordinators were intended to function as change agents at their school i.e. motivating the other teachers. Recruitment of sports-and youth clubs Sports-and youth clubs were automatically included if they met the inclusion criteria. Managers and coaches were informed about their clubs being selected as inter- vention sites in an email with an electronic baseline questionnaire attached. Planning for implementation and sustainability The Boost intervention was implemented from September 2010 to May 2011. Intervention providers included tea- chers, parents, local FV providers, pupils, coaches and managers in sports-and youth clubs, supported by princi- pals, the super market chain, Copenhagen Food house, and the Boost project group. The intervention was designed to be implemented primarily by teachers with minimal help and contact from the research team in order to create a sustainable intervention. All teachers were meant to share the responsibility for implementing the Boost curriculum and FV scheme, supported by the tea- cher(s) coordinating the project at school level. In case of problems with the quantity or quality of FV delivered to schools, teachers were requested to address the local pro- vider to solve issues of concern. The coaches in the sports clubs and the managers of the youth clubs were intended to facilitate increased access to FV in the 13-year-olds’ lei- sure time. Implementation manuals for teachers, pupils, and local FV providers were developed and distributed (teacher manual for curricular activities, teacher manual on conducting school FV breaks, manual on delivery of school FV for schools and local providers, posters for cut- ting up FV snacks and hygiene rules for the school class room). Parental newsletters and club factsheets were used to guide parents and club staff in supporting and promot- ing 13-year-old’s FV consumption. Planning for adoption and dose received among teenagers The following strategies were applied to ensure the pupils’ active engagement in the Boost project: Appealing name, visual identity and pupil workbook, interactive learning i.e. hands on-experiments, computer-based assignments such as computer tailoring, competitions, Boost posters distributed for use in the classroom, time for FV breaks, delivery of class kit with an iPod docking station, and the FV hosting/duty. Page 12 of 25 Evaluation design (step 6) Effectiveness of the intervention will be evaluated employing a cluster-randomised controlled trial design with baseline measurements among pupils, parents and school principals in the beginning of the school year (August 2010), and 1st and 2nd follow-up measurements at the end of the school year (May/June 2011) and one year after (May/June 2012). Trial registration Current Controlled Trials ISRCTN11666034. Power calculations To assess the adequate sample size of schools and pupils needed to detect a 20% difference between intervention- and control schools in intake of FV at follow-up, we calcu- lated the power of a two-sample t-test using the SAS com- puter code suggested by Donner & Klar (1996) [75]. We based intra-class correlations (= 0.01) on Pro Children data. If 20 schools with two school classes of 20 pupils each were randomly assigned to each intervention group, the analyses showed that there would be more than 90% power to detect a 20% increase in pupils’ mean intake of FV between intervention-and control schools (N schools = 40, N pupils = 1,600). Study design, sampling, selection criteria, recruitment, and randomisation Figure 2 shows the flow of the sampling process. We decided on a study design with ten municipalities with two intervention-and two control schools within each municipality. By this study design we aimed at making intervention-and control schools comparable as schools within the same municipality are exposed to the same political context (local health policies and political stand- points). The inclusion of ten municipalities only also reduced travel costs and made fieldwork feasible (e.g. data collection and thorough process evaluation at schools). A simple two-stage cluster sampling process was applied beginning with a random sample of munici- palities (sampling frame: list of all 98 municipalities in Denmark, exclusion criteria: Less than four public schools), followed by a random sample of municipal schools (sampling frame: lists of all schools in selected municipalities). Eligible schools had minimum two school classes of year 7 pupils, exclusion criteria: special needs schools, and private schools. Using a computer-generated list of random numbers we randomly ranked Danish municipalities and the schools within them. The first ten municipalities from the randomly ordered municipal list were selected and within each of them the first four schools from the randomly ordered school lists were drawn. By telephone, principals were invited to take part in the study. They received a letter with factsheets addressing the school administration, teachers, parent board, and pupil council immediately after the telephone