In the field of educational effectiveness research, the influence of a class' student body on students' individual achievement scores has been a popular research interest for many years. Yet, few studies have focussed on the effects of class composition on students' non-achievement outcomes, and up to now, hardly any attempts have been made to summarize the findings of previous studies on this topic by conducting a literature review. The current study tries to fill in this gap and focuses on the effects of class composition in secondary education in terms of ability and gender on students' school well-being and academic self-concept. The results of this literature review indicate that ability grouping is beneficial for strong students' school well-being, but rather detrimental for the school well-being of weak students. The reverse holds for students' academic self-concept. Furthermore, our results show that single-sex classes are advantageous for girls' school well-being and academic self-concept. As for boys, the results are inconclusive. (Contains 2 tables.)