While a number of studies have considered that metacognition is related to processes at an individual level, the role of metacognition during collaborative learning activities remains unclear. Metacognition has been studied mainly as a process of the individual, neglecting the relevance of group regulated behavior during cooperative activities and how group members perceive their skills and reflect on group potentialities. The current study presents the construction and validation of a 20-item quantitative scale for measuring the metacognition of groups based on their knowledge of cognition, planning, monitoring and evaluating. The tool was presented to 362 university students participating in online collaborative activities. The validity and reliability of the scale were verified calculating descriptive statistics, the KMO and Bartlett tests, exploratory factor analysis, Cronbach's alpha, a confirmatory factor analysis and multi-group invariance testing. The findings showed that the instrument is sufficiently valid and reliable. To demonstrate its utility, the scale was used to observe differences in the processes among students attending several courses. Trainee teachers of primary school reported a higher metacognitive level than students in psychology, for example. The findings indicate that metacognition should also be considered in a group dimension rather than only as a reflection of individual behavior, and it should be a relevant construct for understanding online collaborative processes. Ways in which the scale could be applied to improve CSCL and further research for assessing the correlation between metacognition and other constructs are also discussed.