There have been many studies over the past few decades documenting the existence of variable rules in adult language. It is only recently, however, that the acquisition of these rules has been the focus of research, and that event has opened the door for questions about the interaction of the learning of categorical rules and that of variable rules. Specifically, questions have arisen as to whether these rules might not be construed as either a performance factor and/or a reflection of universal constraints on language. The present study examines the acquisition of (-t,d) deletion and (ing) production in 3- and 4-year-old children in order to ascertain their degree of mastery of phonological, grammatical, and social constraints. Seventeen children were tape recorded during play interview sessions in their South Philadelphia day care center. Six to thirteen sessions per child over a three month period were required to obtain sufficient data for analysis. In addition, eight of their parents were interviewed in their homes for purposes of comparison. Results of the study revealed that children as young as three had, for the most part, mastered the process of variation of (ing) and the phonological constraints on (-t,d) deletion, and they were well into the process of acquiring the grammatical constraints on (-t,d) deletion. Their learning of a dialect specific phonological constraint demonstrated that their mastery of this variable rule was not a reflection of universal constraints. Further, their independent analysis of semi-weak verbs made it clear that they were not simply copying frequencies of their parents' forms but learning an abstract rule. The children's acquisition of the extralinguistic constraints on these rules lagged behind that of the linguistic factors. Of particular interest to the issue of gender differences in language was the girls' surprising tendency to delete (-t,d) more often than the boys, demonstrating that they had not yet learned linguistic conservatism in instances of stable variation and arguing against a biological basis for sex-based sociolinguistic differences.