This thesis shows the final results of a longitudinal project where the same participants (12 to 15 yrs.) were followed for three consecutive years. The first objective of this study was to... Show moreThis thesis shows the final results of a longitudinal project where the same participants (12 to 15 yrs.) were followed for three consecutive years. The first objective of this study was to investigate the development of both quantity and quality of metacognitive skills. The second objective was to establish whether the development of metacognitive skills is intelligence-related or relatively intelligence-independent. Finally, the generality vs. domain-specificity of developing metacognitive skills was investigated. While thinking aloud, participants performed two different tasks representing two different domains: A text-studying task and a problem-solving task. Participants__ intellectual ability was assessed, as well as their metacognitive skills and learning performance for both domains separately. In summary, this thesis has shown that (1) Metacognitive skills do increase spontaneously in frequency and quality during young adolescence, albeit not continuously. The various subscales of metacognitive skillfulness do not develop at the same pace; (2) Metacognitive skills have their own contribution to the prediction of learning performance, on top of intellectual ability. The relation between intellectual ability and metacognitive skills as predictors of learning performance is not affected by development between 12 and 15 yrs.; (3) Around the age of 15 yrs. metacognitive skills become fully general. Show less