EN
This article analyzes the relationships between school-based social capital and the average test scores of 9th grade students in Polish middle schools. School-based social capital is understood in terms of supportive communities, and measured on the basis of the youngsters' positive perceptions of the school atmosphere and interpersonal relationships, the support they received from teachers and / or classmates, as well as their assessment of student participation in classroom discussions. Hierarchical linear regression models, estimated on a sample of 63 classes in twenty purposively selected middle schools, found a strong positive relationship between this form of social capital and the average mathematics and science test score.