Disagreement drives metacognitive development.

Metacognition improves significantly over childhood, but the mechanisms underlying this development are poorly understood. We first review recent research demonstrating that disagreement prompts competent responses by young children across several metacognitive domains (confidence monitoring, information search, and source monitoring). We then propose a mechanistic model of how disagreement facilitates metacognition. We localize one main source of children's metacognitive limitations in their still-developing capacities to reason about alternative possibilities, which manifest in an overly narrow focus on one hypothesis. Disagreement increases the child's likelihood of representing alternative hypotheses, thereby promoting improved metacognitive reasoning. The broader proposal is that, through repeated experiences of disagreement, children become better at representing alternative possibilities even when reasoning on their own, leading to metacognitive development.