Small groups in (and out of class) can be used to:

Meyers & Jones (1993)

Be clear about the purposes of group discussion:

Intellectual purposes

To engage students in exploring a diversity of perspectives
To assist students in discovering new perspectives
To emphasise the complexity and ambiguity of issues, topics and themes
To help students recognise the assumptions underlying many of their habitual ideas and behaviours
To increase intellectual agility
To encourage active listening

Emotional purposes

To increase students' affective connections to a topic
To show students that they are heard, their voices matter, that their experiences are valued

Social purposes

Good discussions do not just happen; they usually result from some degree of pre-planning, especially around what and how to contribute.

Brookfield (1990)

Prepare for discussion activities

Choose discussion topics carefully - choose topics that are not too factual or uncontroversial
Provide preparatory materials- access to concepts, ideas, factual information and explanations that will inform their discussion
Evolve consensual rules - create procedural rules and codes of conduct (eg respect minority opinions, no-one is to dominate the group, divergent views are allowed, time limits or maximum contributions allowed)
Personalise discussion topics - connect to student experiences
Introduce some productive dissonance - invite them to consider alternatives