School boards have received little attention in sociology of education. Drawing on organizational sociology, a model of school board social capital is proposed that treats brokerage (external ties) and closure (internal ties) as the key dimensions of board functioning. The model brings together insights from limited research on school boards concerning members' internal and external ties and recasts them as the building blocks of a unifying theoretical framework. It also proposes specific performance outcomes at the district level. The model is tested using the data from a representative sample of Pennsylvania districts. The analysis not only explores brokerage and closure patterns among school boards, but also examines their implications for academic outcomes. Findings suggest that eighth grade reading and mathematics performance are highest in districts, where boards exhibit high levels of both brokerage and closure, and lowest in districts, where brokerage and closure are both low.