Thinking Together is a project that began at the Open University in the mid 1990s and grew out of research that showed that children benefit from explicit instruction on how to talk in groups. Its fundamental premise is that the ability to communicate effectively is a key skill that lies at the heart of educational success. A crucial goal arising from this is to enable teachers and children to conceptualise talk as "thinking aloud with others". In this article, the author discusses his research into collaborative thinking in the primary mathematics classroom.