During the first year of school, student success hinges on learning not only new academic skills, but also behavioral expectations and developing self-regulation skills in the classroom. The purpose of this study was to investigate development in behavioral regulation during the kindergarten year. The authors used multilevel models to explore the association between sex and risk status on academic engagement and disruptive behavior trajectories based on daily teacher-generated behavioral ratings obtained for 22 full-day kindergarten students (six at risk, 12 male) across 80 school days. Results indicated that, in general, behavior improved over time; academic engagement increased whereas disruptive behavior decreased. However, behavioral trajectories varied as a function of sex and risk status. Implications for practice and directions for future research are discussed.