This paper argues for the integration of metacognitive thinking into the content of school science. It describes the ' metacognitive instances ' approach of implanting metacognitive activities, such as classroom discussions, annotated drawing, keeping diary-like notes and concept-mapping, at selected points of the teaching procedure, in an attempt to extend the durability of children's science understanding, which is often short-lived. The approach was tested with 60 Year 5 pupils in Cyprus studying 'Current Electricity', following a quasiexperimental design with one experimental and one comparative group. Following the teaching of the unit, participants were tested on their understanding of electricity three times in one school year. The research showed that the practice of metacognition is feasible with primary school pupils and that children who experienced situated metacognition retained taught concepts for a longer period of time. Although no significant difference was recorded initially in the amount of subject matter learned by the two groups, children who engaged in metacognitive activities appeared to have achieved more permanent re-structuring of their understandings.