Metacognition is an important aspect of human intelligence and higher learning. There is the recognition that metacognition is not just a private internal activity but also socially situated. In this context, the purpose of this research is to develop and validate a metacognitive construct that provides the opportunity to assess metacognition in online discussions. Furthermore, the Community of Inquiry (CoI) theoretical framework provided the conceptual coherence to construct, operationalize and interpret metacognition in an online collaborative inquiry. The results provided evidence of metacognition indicators in student discussion postings and the frequency of these indicators increased over time. (Contains 3 figures and 1 table.)