The purpose of this study is to describe and explain 15 to 19 years old adolescents’ attitudes, knowledge and sexual behavior before and after a sexual health promotion intervention. In addition, the purpose is to examine adolescents’ self-evaluations of the sexual health intervention that was carried out in randomly selected vocational schools. The aim of the study is to produce information that can be used to promote adolescent’s sexual health and to plan, develop and implement sexual health interventions in school environments.

The study was randomized and controlled. Four vocational schools (N = 1104 student places) were randomized in the intervention group, and four vocational schools (N = 800 student places) were randomized in the control group. Research permission was obtained according to the guidelines of each vocational school. The data was collected with a self-completion online questionnaire three times during the study: before intervention in January to February 2011 (baseline n = 705), the first follow-up immediately after the intervention (n=375) and the second follow-up 14 weeks after the intervention (n=161). The duration of the intervention was 11 weeks and it consisted of three components: 1) class-room session of sexual health; 2) information materials (leaflets and posters); 3) free condom distribution. The data was analyzed by statistical methods.

Nearly all participants were 16 to 17 years old (96%). Two thirds of the participants were boys. In the intervention baseline group 63% (n = 432) of the participants wer e sexually experienced and had had either intercourse or oral sex. The condom use was inconsistent among participants. One fifth had been tested for sexually transmitted infections (STI). After the intervention, the proportion of those who had been tested for STIs, was statistically significantly higher in the intervention group. There were no differences in the control group between measurements.

Knowledge concerning sexual behavior was measured with eight questions. Before the intervention on average five questions were answered correctly. The least well-known questions were related to the symptoms of STIs and to the transmission of HIV-infection. Boys had statistically significantly weaker knowledge than girls. In the intervention group the knowledge was statistically significantly better in the second follow-up group than in the first follow-up group. In the control group the participants had significantly higher knowledge in the second follow-up compared with the baseline or with the first follow-up gro up.

Attitudes concerning sexual behavior were measured as total and in four subcategories: 1) self-efficacy in condom use 2) self-efficacy in communication 3) feeling of social acceptance 4) obstacles to condom use. Before the intervention, the attitudes concerning sexual behavior were positive in all four sub-categories. The mean total score of the attitudes was statistically significantly lower, and there were less positive attitudes in the first follow-up intervention group compared to the other groups. There were no statistically significant differences concerning attitudes in the control group.

The participants were fairly satisfied with all the components of the intervention: class-room session, information materials and free condom distribution. More positive evaluation from the class-room session was significantly associated with being in a relationship. The positive self-evaluation of information materials and condom distribution was most frequently associated with the perceived access to the school health nurses’ appointment.

Young people's sexual behavior seems to be active and diverse, but condom use is inconsistent. Especially in oral sex or in anal intercourse a condom is rarely used. The diversity of sexual behavior among adolescents should be taken into account in sexual education and find new ways to motivate adolescents to use condoms and to be tested for STIs. Adolescents, especially boys, have weak knowledge concerning sexual behavior. Adolescents knowledge concerning sexually transmitted infections such as HIV should be strengthened. Adolescents’ attitudes concerning sexual behavior are positive, which is a good starting point for sexual health promotion.