Self-determination theory (SDT), when applied in education, emphasizes helping learners internalize extrinsic motivation so as to regulate their learning behavior from an amotivation state to intrinsic motivation. The purpose of this study was to examine the relationship between SDT components and learning in middle school physical education. Sixth grade students (n = 242) from 15 randomly selected schools provided data on SDT and their knowledge and skill learning achievement as assessed using a pre- and post-measurement design. Structural equation modeling analyses revealed that extrinsically regulated motivations and intrinsic motivation contributed little to knowledge and skill achievement and amotivation negatively related to knowledge improvement. Given the fact that the data represented learner responses to an activity centered program, the findings imply that when learning objectives are vague, learners may be motivated to participate in classes but their participation may not contribute much to knowledge and skill achievement. (Contains 1 table and 2 figures.)