Why do parents parent the way they do?'' remains an important question since it concerns both scientific issues, such as the stability or change of childrearing behavior, and clinical issues, such as the way to promote positive parenting in evidence-based programs. Using an accelerated design, the aim of this study was to examine several parental and child predictors of childrearing behavior trajectories among 373 mothers and 356 fathers of 2-to 9-year-old children. Hypotheses were drawn from Belsky (1984) and subsequent studies of the determinants of parenting. The parental and child predictors were assessed and analyzed as time-varying (parental self-efficacy beliefs and child externalizing behavior) or time-invariant (parental educational level and personality traits) predictors, according to their conceptual properties. The results show a linear decrease in both supportive and controlling childrearing behavior in mothers and an improvement in supportive but a decrease in controlling childrearing behavior in fathers over time. Moreover, the results support the idea that childrearing behavior is determined by multiple factors, in particular the parents' self-efficacy beliefs and the child's behavior. Finally, the results confirm the hypothesis of a greater influence of child predictors than of parental ones in the case of mothers, while the reverse hypothesis of a greater predictive power of parental variables than of child ones is confirmed for fathers. The results are discussed both for research and clinical purposes.