While important evidence suggests many health-related behaviors may be subject to strong peer influences, less is known about teenage girls’ fertility outcomes, including pregnancy and childbearing.  In this paper, we present a set of instrumental variable and reduced form results that suggest that the likelihood of having a teenage pregnancy is influenced by peers.  We show that the instruments, the proportion of peers with teenage mothers and the average peer age of menarche, are plausibly exogenous across cohorts of students who are attending the same high schools.  The peer effect estimates are large—a 10 percentage point increase in peer pregnancies is associated with an increased likelihood of pregnancy between 2-5 percentage points.  We show that peer influence is greater in environments that have other policy factors that also increase teenage pregnancy rates, such as lack of contraceptive services in schools.  Finally, we show suggestive evidence that the peer effects operate primarily through shaping social norms rather than information or knowledge sharing mechanisms.  Our results suggest that policies targeting social norms and expectations regarding the timing of entry into parenthood may be able to leverage social multipliers in reducing the rate of teenage pregnancies.