<p>This study aimed to investigate the trajectories of students’ self-regulated learning in an online course and the predictive role of students’ satisfaction with basic psychological needs (autonomy, competence, relatedness) on these trajectories. Additionally, the potential variation in the relationship between basic psychological needs and self-regulated learning based on students’ achievement levels was examined. The analysis of data revealed a significant increase in students’ self-regulated learning scores throughout the three-month course. Data from 1,105 elementary and middle school students participating in an online learning program were collected over four 12-week periods. This study confirmed the increase in learners’ self-regulated learning in an online learning environment over a 12-week period. The study found that autonomy, competence, and relatedness were related to the initial value of self-regulated learning but did not significantly influence the growth of self-regulated learning over the course. The study also found that the relationship between basic psychological needs and self-regulated learning varied among different achievement groups. Autonomy and competence played a significant role in predicting the initial level of self-regulated learning in all groups, regardless of achievement level, whereas relatedness had the most substantial effect for the high-achieving group.</p>