Although existing research mostly supports the association between school climate and academic achievement, the processes and factors that underlie this correlation are less explored. We rely on social-cognitive theory and the concept of academic self-efficacy to test a model in which academic self-efficacy mediates the association between school climate and academic achievement in a sample of 1,641 middle and high school students in Israel. The participants filled out measures of academic self-efficacy as well as a school climate questionnaire yielding 3 sub-scales describing interpersonal relations, violence, and sense of belonging. We also collected students' grades in mathematics and English as well as self-report assessment of academic achievement. The results supported the model, with 2 of the 3 climate sub-scales (interpersonal relations and belonging) positively associating with self-efficacy, which in turn associated positively with all 3 measures of achievement. The results may add to our understanding of the underlying dynamics accounting for the association between organisational-level characteristics and individual performance in schools.