The purpose of this study was to examine self-determination outcome data in the year following a one-year cluster randomized controlled trial (C-RCT) comparing the impacts of a Self-Determined Learning Model of Instruction (SDLMI) only condition to a SDLMI + Whose Future Is It? (SDLMI + WF) condition. Using multilevel B-spline model analysis with Bayesian estimation, we examined ongoing patterns of growth after the trial ended and all students were exposed to SDLMI + WF. The findings suggest that the inclusion of an additional year of outcome data provided additional insight into the impact of more intensive intervention conditions over time. Specifically, after the initial year of implementation, the SDLMI + WF condition predicted greater annual gains than the SDLMI only condition, unlike findings in the first year which reflected the opposite pattern. This evidence suggests a nonlinear growth pattern over multiple years of intervention with more intensive interventions. Implications for future research and practice are discussed.