Krølner et al. BMC Public Health 2012, 12:191 http://www.biomedcentral.com/1471-2458/12/191 compromised by the project groups’ active involvement in the FV programme. We were responsible for the selection of FV delivered to the schools each month. Our intention was to ensure that year 7 pupils at all intervention schools were exposed to a variety of FV, preferably organic, Danish and in season. The downside of this approach is that nobody takes on this task after the termination of the research project at the schools. Implications for research It remains a challenge to ensure sufficient implementa- tion when intervening in schools. The comprehensive examination of implementation processes, barriers and facilitators in the Boost study may contribute with impor- tant insights on how to promote implementation of school-based interventions. The systematic and theory- based approach to process evaluation taken in this study may guide development of future process evaluations in intervention studies and yield important knowledge. The incorporation of a data collection in the computer tailor- ing module is tested in our study and may be a promising tool to inform future process and effect evaluations. The Boost study will provide answers to whether it is possible to disentangle the effects of different components by ana- lysing effects on proximal outcomes (determinants) and will attempt to monitor the dose received of each inter- vention component. Also the separation of fruit and vegetables as different outcomes may illuminate whether the strategy of targeting fruit and vegetables in the same intervention is an effective way to increase both fruit and vegetable intake. The detailed 24-hour recall data col- lected at all three time points enable analyses of changes in intake of specific types of FV. Finally, intake of specific types of FV can be analysed in relation to data about which types of FV the pupils received through the school FV programme. Implications for practice The Boost project will provide new knowledge on the effectiveness of school-, family-and community-oriented strategies to increase FV intake among teenagers. This awareness may constitute a valuable basis for evidence- and practice-based recommendations to stakeholders. A strong environmental component like free provision of FV is highly dependent on funding and community priorities nationally and locally. An important part of the evaluation will be to sum up the costs of the various intervention components to inform stakeholders and health plan administrators. The analysis of the effect of the interven- tion in different social groupings will provide valuable information to politicians on possibilities to decrease social inequality in FV intake. To promote the implementation of the intervention at schools the curricular activities were designed to be implemented in different subjects so the Page 22 of 25 teachers could share the assignment instead of only one teacher being responsible for the curriculum. The process evaluation will illuminate whether this is an approach to be recommended in health promotion initiatives. It is challenging to reach schoolchildren in their leisure time due the large variety of activities and settings which they utilise. One fifth of the teenagers in the Boost study does not attend a youth-or sports club and sports-and youth clubs have very different facilities, policies and con- ditions. The process-and effect evaluation of the Boost lei- sure time intervention component will illicit valuable information about the opportunities and barriers for health promotion in this setting and may serve as a pilot study for more intensive, future interventions. Funding sources The Boost study is part of Centre for Intervention Research in Health Promotion and Disease Prevention, National Institute of Public Health, University of Southern Denmark, Øster Farimagsgade 5A, 1353 Copenhagen K, Denmark. The Centre is funded by TrygFonden and the Danish Cancer Society. The Boost study is funded by a 5- year donation from TrygFonden including funding of each author and coverage of expenses related to intervention, implementation and evaluation. PhD scholarships for AKA and TSJ are co-financed by University of Southern Denmark. The free FV school scheme was co-financed by 1) FDB and 2) the EU School Fruit Scheme through the Danish Food Industry Agency at the Danish Ministry of Food, Agriculture and Fisheries. Copenhagen Food House contributed financially to the development of the teaching material. Acknowledgements The Boost project group would like to thank all participating schools, schoolchildren, parents, teachers, principals, and representatives from youth- and sports clubs. We thank FDB, Coop and local FV providers for their donation and help with FV delivery. We would like to express our gratitude to everyone who has allowed us to use extracts from their educational material for the creation of the Boost teaching material. We thank the Boost International Steering Committee for sharing their expertise. We would like to acknowledge national and international colleagues who have contributed to the development, data collection implementation, and evaluation of Boost. We would especially like to thank the following people for their contribution: Nanna Lien, Mona Bjelland, Maria Bruselius-Jensen, Bent Egberg-Mikkelsen, Morten Peytz, Rasmus Gøtsche, Helle Brønnum-Carlsen, Simon Rask, Morten Strunge Meyer, Iben Nowak, Susanne Tøttenborg, Ida Husby, Finn Diderichsen, Mogens Trab Damsgaard, Michael Davidsen, Mikael Beck, Olaf Rieper, Sanne Schnell Nielsen, Jens Aarby, Mette Rasmussen, Ida Monrad, Sanne Jørgensen, Julie Aarestrup, Lea Trier Krøll, and Laura Camilla Thordahl. The Boost computer tailoring was developed in cooperation with Marianne Wind and Willemieke Kroeze, funded by TrygFonden. Finally, we would like to thank Professor Bjørn Holstein for constructive comments to an earlier draft of this manuscript. Author details 1Centre for Intervention Research in Health Promotion and Disease Prevention, University of Southern Denmark, National Institute of Public Health, Øster Farimagsgade 5A 2nd floor, 1353 Copenhagen K, Denmark.