This study assessed preschool children's (N= 52) ability to introspect and monitor their own levels of certainty. After a book reading intervention, children reported that they were less certain of answer choices in a picture identification game. School differences showed that some groups of children reported improved levels of certainty monitoring, while other groups of children reported scores dissimilar to those predicted. This indicated that children who were immersed in rich learning environments, where strict curriculum and emotion understanding training were enforced, could be predisposed to this type of certainty understanding.

Understanding sources of knowledge (e.g., seeing leads to knowing) is an important ability in young children’s theory of mind development. The research presented here measured if children were better at reporting their own versus another person’s knowledge states, which would indicate the presence of introspection. Children had to report when the person (self or other) had knowledge or ignorance after looking into one box and not looking into another box. In Study 1 (N = 66), 3- and 4-year-olds found the other-version of the task harder than the self-version whereas 5-year-olds performed near ceiling on both versions. This effect replicated in Study 2 (N = 43), which included familiarization trials to make sure children understood the question format. This finding is in support of the presence of introspection in preschool-aged children. In the same studies, children also showed evidence for theorizing about their own and others knowledge states in a guessing task (Study 1) and in true and false belief tasks (Study 2). These findings together indicate both introspection and theorizing are present during young children's theory of mind development.