Research Findings: Behavioral self-regulation is crucial for school success. Although behavioral self-regulation typically grows rapidly during the preschool period, children in this age group vary widely in their behavioral self-regulation capacities. The present study investigated 3 potential determinants of growth rates in behavioral self-regulation in children from an affluent region in Germany: family educational resources, child gender, and child negative affectivity. Using a longitudinal design, we observed children (N = 60) during the last 2 years before school entry. Children from families with relatively fewer educational resources started off with a lower level of behavioral self-regulation and did not catch up with their more advantaged peers. Boys showed poorer initial behavioral self-regulation than girls, but their gains in behavioral self-regulation were greater over time compared to girls'. Negative affectivity influenced neither the initial level of nor growth in behavioral self-regulation. Practice or Policy: The present findings suggest that even in a relatively affluent region differences in families' educational resources influence children's behavioral self-regulation trajectories. At least in the German context, early interventions to facilitate behavioral self-regulation in children from families with comparatively fewer educational resources should be a focus of policies attempting to reduce achievement gaps.