Three propositions that are central to J. R. Harris's group socialization theory (1995, 1998) are considered in this review. These propositions are as follows: (a) Parental behaviors have no long-term effects on children's psychological characteristics, (b) peer groups are the primary environmental influence on psychological functioning, and (c) dyadic relationships are situation-specific and do not generalize. The evidence that J. R. Harris has outlined in support of each of these propositions is reviewed, as is additional empirical research not considered by J. R. Harris. Serious limitations to each proposition are identified. The available evidence is more consistent with a model of multiple socialization agents. An expanded research agenda that permits a more definitive test of J. R. Harris's propositions and social relationship theory is proposed.