This article gives an overview of developmental trends in research on metacognition in children and adolescents. Whereas a first wave of studies focused on the assessment of declarative and procedural metacognitive knowledge in schoolchildren and adolescents, a second wave focused on very young children's "theory of mind" (ToM). Findings from a recent longitudinal study are presented that demonstrate developmental links between early ToM and subsequent declarative metacognitive knowledge, mainly mediated by language competencies. The relevant literature further indicates that developmental trends in declarative and procedural metacognitive knowledge clearly differ. Whereas the findings for declarative metacognitive knowledge show steady improvement through childhood and adolescence, mainly due to increases in knowledge about strategies, the results are not similarly clear-cut for procedural metacognition. Age trends observed for this component of metacognition are significant for self-control activities but not pronounced for monitoring abilities. These findings have important implications for education, emphasizing the role of strategy training procedures in different instructional domains and illustrating teachers' potential impact on the improvement of monitoring and control processes.