The investigation examined the developmental components of the Nicholls' theory of achievement motivation. Specifically, children's understanding of luck and skill in the physical domain. The sequent attribution tendency was discussed too. Subjects were 152 students age from 8-10 years (eight 52, night 48, ten 48). Subjects were asked to engage dart- throwing practice three cycle, fifteen times a cycle. The practice was separated into three parts: practice task, skilled task and luckily task. Before and after the dart-throwing practice, subjects were interviewed. The results were consistent theoretical predictions and indicated that (1) Children's understanding of luck and skill in the physical domain has four stages. Furthermore, (2) there was a significant positive correlation between age and the maturation of understanding luck and skill. In other words, there was a tendency for subjects to have a more mature understanding luck and skill when children were getting older. On the other hand, (3) there was a tendency for subjects to have a less mature understanding luck and skill signally attributed the success or failure to "effort and competence" on the luckily task. (4) On contrast, the "luck and difficulty" factor was more attributed when it was higher.