Student Networks and Long-Run Educational Outcomes: The Strength of Strong Ties

The aim of this paper is to investigate and understand the effect of high-school friends on years of schooling. We develop a simple network model where students first choose their friends and then decide how much effort they put in education. The empirical salience of the model is tested using the four waves of the AddHealth data by looking at the impact of school peers nominated in the first two waves in 1994-1995 and in 1995-1996 on the educational outcome of teenagers reported in the fourth wave in 2007-2008 (when adult). We find that there are strong and persistent peer effects in education but peers tend to be influential only when they are strong ties (friends in both wave I and II) and not when they are weak ties (friend in one wave only). We also find that this is not true in the short run since both weak and strong ties tend to influence current grades.