This article examines how teachers and parents in 10 municipal schools serving students growing up under conditions of social vulnerability represented themselves, and others, as valid agents for charting school improvement. In four schools parents and teachers saw each other as trustworthy and collaborating to provide an education that could transform students' life chances. In the other six schools, social relations were marked by distrust, staff constructed students as lacking the resources necessary to benefit from a rigorous academic programme, and parents in leadership positions shared with teachers the belief that school failure could largely be attributed to uncommitted parents. These results suggest that the impact of quality assurance policies tends to be associated with the social capital of municipal schools, thus educational policy needs to consider developing and strengthening social capital within schools. (Contains 1 table and 3 notes.)