Defining and therefore evaluating the effectiveness of school sex education is problematic because of its location at the site of struggle between competing discourses. Those discourses--summarised here as "moralistic," "harm reductionist" and "empowering"--each emphasise a different conceptualisation of sex education's intended outcomes. The challenges that these discursive tensions present for research are examined by drawing on a study investigating the effectiveness of involving young mothers in school sex education. Through a discussion of some of the study's findings, the value of adopting a multi-method approach as a way of managing different understandings of effectiveness is explored. The article concludes that research in the area of sex education needs to make use of complex study designs, which take into consideration these contested understandings regarding its purpose. (Contains 2 notes and 2 tables.)