This paper uses administrative data from the University of Texas-Austin to examine whether high school peer networks at college entry influence college achievement, measured by grade point average (GPA) and persistence. For each freshman cohort from 1993 through 2003 we calculate the number and ethnic makeup of college freshmen from each Texas high school, which we use as a proxy for freshmen “peer network.” Empirical specifications include high school fixed effects to control for unobservable differences across schools that influence both college enrollment behavior and academic performance. Using an IV/fixed effects strategy that exploits the introduction and expansion of the Longhorn Scholars Program, which targeted low income schools with low college traditions we also evaluate whether “marginal” increases in peer networks influence college achievement. Results show that students with larger peer network upon entering college perform better than their counterparts with smaller networks at the beginning of their freshman year. Average effects of network size on college achievement are small, but a marginal increase in the size of same-race peer networks raises GPA by 0.1 point. We also find some suggestive evidence that minority students with large high school peer networks reap larger academic benefits than their white counterparts