This project develops a revision of 'Long Live Love' (LLL], a program aimed at prevention of sexual risks among secondary school students and systematically investigates its effectivity in comparison to the present, outdated version. In addition, effectivity of systematic pre-implementation and folluw-up teacher training is evaluated. The revision will specifically address different educational needs of girls versus boys and of students of Dutch versus non-Dutch origin. In randomized control TRIAL ONE, 120 classes (25 students each) are randomly assigned to three conditions: 1) revised program + pre-implementation teacher training; 2) revised program; 3) old program. In randomized control TRIAL TWO, 80 classes will be randomly assigned to 2 conditions: 1) additional follow-up teacher training, feedback and in-person assistance and 2) pre-implementation training only. Short- and longterm differential effects in terms of relevant cognitions, skills and behavioural intentions will be analysed on class and individual level.