This paper reviews Diana Baumrind's studies of the effect of various types of parental control on children's behavior and concludes that a child is more likely to develop a sense of competence, responsibility, and independence if he or she is given firm and reasonable guidelines. A brief survey of Baumrind's first two studies of preschool children and their parents indicates that, in association with other factors, firm parental discipline makes for competent children. Baumrind's third project, a longitudinal study of 150 children enrolled in nursery school in 1967 and their well-educated, middle-class families is examined in greater detail. The phase of research reported here was on the effects of different kinds of parental discipline upon children's instrumental competence (social responsibility, independence, orientation to succeed, and vigor). Three major types of parents were identified in this study, each having different effects on preschool children: (1) authoritarian (values obedience and the preservation of order; restricts the child's autonomy; no give or take); (2) authoritative (directs child's activities firmly, consistently and rationally; sets standards, but does not regard self as infallible); (3) permissive (gives child as much freedom as is consistent with child's physical survival). Children of authoritative parents were found to be most competent in nursery school. A follow-up study of 96 of the children and their parents when the children were between 8 and 9 years old indicated that, as before, children of authoritative parents were most competent. (CM)