In an effort to enhance both adolescents' social capital and increase achievement, public school districts across the United States have created small high schools. Using data derived from a longitudinal and nationally representative study of U.S. high school students, the Educational Longitudinal Study of 2002, results show that when adolescents' parents know their friends' parents math achievement is significantly predicted. This association, however, is nonsignificant when conditioned on standard measures of prior achievement and family background, among others. In addition, while this relationship is also strong and significant within small high schools, it, too, is eliminated when conditioned on select confounding variables. These findings are discussed in terms of current efforts to improve achievement through reductions in school size. (Contains 3 tables.)