This article considers how students might work together in small groups, from two to eight, in either a primary or secondary science classroom. The nature of group work can vary widely and could include, for example, a pair carrying out an illustrative experiment, a trio or quad debating climate change, or six or seven rehearsing how they will enact the movement of particles within a solid, liquid and gas. There are different forms of social interaction during group work. It may be working "co-operatively" (students working on individual tasks, and then sharing outcomes with other group members); "collaboratively" (participating in joint activity, which is mutually supportive, working towards a common goal and developing shared understanding); engaging in "peer tutoring" (where more expert students structure and support the work of less expert); or formative "peer assessment" (where a peer critiques another's work and offers constructive modifications). This article outlines factors influencing the occurrence, type and effectiveness of group work and suggests "what next" regarding extending, enhancing or enriching effective group work in science classrooms. (Contains 4 notes.)