This study investigated the construct validity of a Norwegian version of a scale measuring intrinsic and extrinsic motivation. Furthermore, mean level differences of intrinsic and extrinsic motivation in three grade levels of students (8th and 10th grade of lower secondary school and 1st grade of upper secondary school) were investigated. Finally, this study investigated how students' level of perceived academic achievement correlated with intrinsic and extrinsic motivation. Factor analysis based on the total sample (N = 3203) supported a one-factor solution for intrinsic motivation and a three-factor solution for extrinsic motivation. The students at all grade levels had a significantly higher mean level of extrinsic than intrinsic motivation. There were significant grade level differences in mean levels of intrinsic motivation and in the subscales of extrinsic motivation. Students' perceived academic performance correlated positively with intrinsic motivation, but also with subscales of extrinsic motivation.