Krølner et al. BMC Public Health 2012, 12:191 http://www.biomedcentral.com/1471-2458/12/191 independent of sociodemographic characteristics (popu- lation-based preventive strategy) but the special needs of vulnerable groups were taken into account by target group analysis among boys and adolescents from low income homes. Target group analysis We conducted two gender-homogeneous focus group dis- cussions, one with boys (N = 8) and one with girls (N = 8) from year 7 in a Danish school with a high proportion of children from low income families. The focus groups were designed to explore perceptions and experiences with bar- riers and facilitators for eating FV, as well as the target groups’ views on the relevance and appeal of our initial intervention ideas and strategies. In agreement with stu- dies from other countries [6], the adolescents emphasised home availability, school availability, price, taste, food pre- paration, and appeal as influencing their intake. To help guide our selection of communication channels and devel- opment of visual identity and intervention tools two school classes of year 7 pupils from the same school com- pleted a short questionnaire on their favourite dishes, hob- bies, music, books, use of cell phone, time spent on computer, and memberships of internet forums and sports-and youth clubs. Parents at the same school were invited to participate in a parent focus group to illuminate parental barriers and ways to involve parents in interven- tions. Only one parent accepted our invitation and was interviewed face-to-face. Finally, we carried out observa- tions at one school during lunch breaks to observe the year 7 pupils habits and activities. Setting The Danish school system All children are entitled to free tuition at Danish munici- pal primary and lower secondary school. This tuition includes a one-year, pre-school class followed by nine years of primary and lower secondary school. Private schools exist where a small part of the tuition is paid for by the parents. Most children in Denmark (86% in 2008) attend the municipal primary and lower secondary school [52]. Children automatically attend a municipal primary and lower secondary school in the area where the family lives. Children will often stay in the same school class throughout their school education. Schools have a board that includes school representatives and representatives elected by the parents themselves. Pupils have the oppor- tunity to influence their school by forming pupil councils to inform important school decisions. There is no national provision of school meals. Children usually bring their own lunch bag or buy lunch in a school can- teen if available [52,53]. Outside school hours Youth schools, recreational junior-and youth clubs All Danish municipal authorities have youth schools for Page 4 of 25 adolescents aged 13 to 18. The Youth School is a special Danish education form, where youth can supplement their school education in their spare time. Enrolment is voluntary and tuition is free. Youth schools are open in the afternoon and evening, and here it is possible to take academic and creative subjects such as music, photography, learn about IT or simply hang out with other young people. Some municipal authorities also have recreational clubs adolescents can attend when they have outgrown municipal after-school centres or after-school care schemes some of which must be paid for by participants [53]. Here we use ‘youth clubs’ as an umbrella term for both youth schools and recreational clubs. Local sports associations and sports clubs In Denmark almost two thirds of all children and adolescents are engaged in organised sports in their leisure time. They are all run by a committee elected by the members. Association life is mostly based on voluntary, unpaid work by managers and coaches [54]. Project name and visual identity The project was named ‘Boost’ to indicate energy and power. The intervention was designed to boost the adoles- cents’ FV intake and energy level. Names in English appeal to Danish teenagers and the intention was to make the 13- year-olds perceive the project as ‘cool’. The logo was also designed to express vitality and with a humorous tone to appeal to the adolescents. Programme theory and outcomes The programme theory (Figure 1) was guided by systema- tic reviews of determinants of adolescents’ FV intake, reviews of intervention studies, theory, experiences from recent successful or innovative intervention studies, espe- cially the international Pro Children study and the Norwe- gian Health In Adolescents (HEIA) study [3,6,39,55-57], input from the planning group and international steering committee, and discussions with the target group. In agreement with best practice, the programme theory out- lined the causal chain which explains how the intervention is expected to impact distal outcomes (FV intake) through changes in proximal outcomes (determinants). We con- ducted a brainstorm and prioritisation of important and changeable determinants of adolescents’ FV consumption identified from systematic literature reviews [3,6]. As shown in Figure 1 the intervention was designed to pro- duce changes in environmental, social and personal deter- minants. We hypothesised that the effect would differ by gender and SEP because of the low FV intake among boys and low income children [3]. Likewise we hypothesised that the effect of the intervention would differ by imple- mentation degree. Furthermore, the programme theory (Figure 1) mapped out unintended adverse effects as well as anticipated potential positive side effects of the intervention [58]