Teens tend go to bed later, get less sleep, and report more daytime sleepiness. Medical research emphasizes biological determinants of teens' disrupted sleep (i.e., the timing of puberty and resultant drops in melatonin), rarely or inadequately considering youths' social ties as a determinant of sleep behaviors. Sociologists recognize how social ties affect health behaviors but have generally neglected sleep, especially among teens. Drawing on a sample of 974 teens from the Study of Early Child Care and Youth Development, this study controls for developmental and social relational factors to predict changes in youths' sleep patterns between 12 and 15 years of age. In general, social relational factors outperform developmental factors in determining youths' sleep patterns, particularly pointing to the importance of parental, peer, and school ties in promoting healthy sleep behaviors. The implications of these findings for further research are briefly discussed.