BackgroundSexual harassment is a widespread problem with serious consequences for individuals and societies. It is likely that sexual harassment among peers has its main onset during the transition from late childhood to early adolescence, when young people enter puberty. However, there is a lack of systematic research on sexual harassment during this developmental period. Thus, there is very little information about the prevalence of sexual harassment during this important transition, its consequences, and how to effectively intervene against and prevent the problem. The primary objective of the described project, entitled Peer Relations In School from an Ecological perspective (PRISE), is to examine sexual harassment and its developmental correlates during the transition from late childhood to early adolescence.MethodsThe PRISE study has a longitudinal design over 3 years, in which a cohort of children (N = 1000) and their main teachers (N = 40) fill out questionnaires in grades 4, 5, and 6. The questionnaires assess aspects of peer sexual harassment and potential correlates including biological (e.g., pubertal development), psychosocial (e.g., self-assertiveness, self-image, peer relations), and contextual (e.g., classroom climate, norms) factors. In addition, we will examine school readiness and policies in relation to sexual harassment and collect register data to assess the number of reports of sexual harassment from the participating schools.DiscussionThe PRISE study will enable the researchers to answer fundamental, unresolved questions about the development of sexual harassment and thus advance the very limited understanding of sexual harassment during the transition from childhood to adolescence - a central period for physical, sexual, and social development. Due to the sensitive nature of the main research concepts, and the age of the participants, the ethical aspects of the research need particular attention. Ultimately, the hope is that the PRISE study will help researchers, policy makers, and practitioners develop, and implement, knowledge that may help in combating a major, current societal challenge and adverse aspect of young people’s developmental ecologies.