The main purpose of the present research was to investigate school intrinsic and extrinsic motivation, and amotivation as a function of age in a sample of 1,600 elementary and high school students aged 9-17 years. First, results revealed a systematic decrease in intrinsic motivation and self-determined extrinsic motivation from age 9 to 12 years, a slow stabilization until 15 years old, followed by an increase after that point. Second, non self-determined extrinsic motivation showed a decrease up to 12 years old and a slow stabilization after that point. Finally, amotivation was relatively low and stable from age 9 to 17 years. Of importance is that the present results also revealed that teacher autonomy support mediated the age-school motivation relationships. The present results underscore the importance of a better understanding of the mechanisms through which lower intrinsic motivation and self-determined extrinsic motivation in older students take place, eventually leading to appropriate interventions and optimal motivation in students of all ages.