The results of international comparative studies have shown thatrelationships exist between metacognition and cognitive activation andlearning success. Since 2007 we have been carrying out projects inIndonesia to improve cognitive and metacognitive activities of pupils ofyear 7 and their teachers. These activities are to contribute to theconstruction and sensible use of sustainable mental models formathematical concepts and methods by learners.This paper shows how games are used for the enhancement of metacognitive and discursive activities in class. Their effectiveness isdocumented exemplary by means of students’ outcomes and transcriptsof lessons from project classes.