In this study, we investigated students' views on themselves as learners of mathematics as a function of school-by-sex (N = 2034, MAge = 18.49, SDAge = 1.25; 12th-grade; 58.2% girls). Using latent variable Structural Equation Modeling (SEM), the measurement and structural equivalence as well as the equality of latent means of scores across single-sex and coed schools were tested. Findings regarding the latent mean differences revealed that girls in single-sex schools had significantly higher mathematics self-confidence than did students' in coed schools. Girls in coed schools had significantly lower mathematics self-concepts than did boys in single-sex, girls in single-sex and boys in coed schools. Girls in single-sex schools had significantly higher family encouragement than students' in all other school types. Moreover, a more complex dynamics were found on the teacher quality variate. This paper argues for a deeper understanding of sex-school interaction and of possible causes of students' views on mathematics.