This paper explores the effect of the human capital characteristics of co-ethnic immigrant communities on foreign-born students' math achievement. We use data on New York City public school foreign-born students from 39 countries merged with census data on the characteristics of the immigrant household heads in the city from each nation of origin and estimate regressions of student achievement on co-ethnic immigrant community characteristics, controlling for student and school attributes. We find that the income and size of the co-ethnic immigrant community has no effect on immigrant student achievement, while the percent of college graduates may have a small positive effect. In addition, children in highly English proficient immigrant communities test slightly lower than children from less proficient communities. The results suggest that there may be some protective factors associated with immigrant community members' education levels and use of native languages. [ABSTRACT FROM AUTHOR]