Need for Cognition has been established as a key intellectual investment trait shaping students' academic development. However, little is yet known about its malleability, particularly in youth. This study investigated stability and change in Need for Cognition in a large longitudinal sample of 3409 adolescents from 166 classes in 27 schools in Flanders. Participants reported on their Need for Cognition in Grades 7, 8, 11 and 12. First, the latent rank-order stability of Need for Cognition between Grades 7 and 11 was found to be r = 0.50. This stability was of a similar magnitude to that of the Big Five personality traits observed in the same sample and larger than that of academic intrinsic motivation. Second, trajectories of Need for Cognition over time were found to vary between individuals. In particular, three trajectory classes could be identified, differentiated mainly by the initial level of Need for Cognition (i.e., a low, medium, and high trajectory). Finally, cognitive ability, cognitive stimulation at home, and parental autonomy support, but not parental educational level, were associated with higher odds of belonging to the high Need for Cognition trajectory and lower odds of belonging to the low Need for Cognition trajectory.