This study focuses on the implementation of sex education in Portuguese schools, between the 7^th and 9^th grades, according to a bio-ecological approach (Bronfrenbrenner, 2005) and the biographic and professional model of sex education (López, 2005).  Although ecological models have been increasingly applied to health behaviors and health education (e.g., McLeroy, Bibeau, Steckler, & Glanz, 1988; Salazar et al., 2010), little research has looked at sex education from an ecological view (Eisenberg, Madsen, Oliphant, & Resnick, 2012). This model has been evinced as well-suited because it allows considering sex education from a broader and complex view and exploring cross-level influences (Einsenberg et al., 2012), avoiding a narrow understanding of relevant factors for its implementation. So sex education is one of the major proximal processes of psychosexual development, and, as proximal process, it is influenced by several systems, from the chrono and macrosystems to the school microsystem. Nonetheless, the factors affecting sex education implementation in schools are less explored (UNESCO, 2010), particularly the factors from multiple levels.

The main research question of the current study is: which factors affect school-based sex education implementation in Portugal? The study goals are: to know how schools really plan, implement and evaluate sex education; to explore the factors that contribute to successful implementation of effective school-based sex education; to explore barriers or challenges for sex education implementation; and to explore cross-level influences.

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