The research about group work in classrooms tells us that we shouldn’t just put pupils into groups and ask them to talk. For it to be productive, and to impact on learning, pupils need to learn the skills of how to talk well in groups.
When starting this, one first step is to keep groups small. Start with trios.
More on talking in groups
A book exploring another helpful structure to promote high-quality talk
The importance of taking a moment to look and listen carefully