Previous work has shown that school achievement is lower in children living in poor neighborhoods. In this study, the authors hypothesized a role of neighborhood social capital. Data on 11-year-olds were obtained from the baseline measurements of a family cohort study (n = 328). The data had a cross-level structure: neighborhood level, school level, and individual level. After including individual-level confounders, neighborhood socioeconomic disadvantage and social cohesion were not associated with school achievement in boys or girls. However, lower levels of neighborhood informal social control were associated with lower school achievement scores in boys only. In boys, a wider social environment that contributes to obedience to norms and values may be conducive to superior educational achievement. (Contains 4 tables.)