Long After They're Gone? The Effect of Peers on Outcomes of Young Adults

A variety of public campaigns, including the “Just Say No” campaign of the 1980s and 1990s that encouraged teenagers to “Just Say No to Drugs”, are based on the premise that teenagers are very susceptible to peer influences. Despite this, very little is known about the effect of one’s peers in middle school and high school on the long-run outcomes of children. This is primarily due to two factors: the absence of information on peers merged with long-run outcomes of individuals and, equally important, the difficulty of separately identifying the role of peers. This paper studies this issue using data on the population of Norway and idiosyncratic variation in cohort composition within schools to examine the role of peer composition in 9 grade on longer-run outcomes such as IQ scores at age 18, teenage childbearing, post-compulsory schooling educational track, adult labor market status, and earnings. We find that outcomes are influenced by the proportion of females in the grade and these effects differ for men and women. There is little evidence that other peer variables (average age, proportion firstborn, average mother’s education) have any impact on the outcomes of teenagers. * Devereux thanks the Irish Research Council for the Humanities and Social Sciences (IRCHSS) for financial support. Black and Devereux gratefully acknowledge financial support from the National Science Foundation. Salvanes thanks the Research Council of Norway for financial support. We would like to thank Eve Caroli and Eric Maurin for helpful conversations. We are indebted to Stig Jakobsen who was instrumental in obtaining data access to the IQ data from the Norwegian Armed Forces.