A pyramid discussion is a speaking activity where learners form progressively larger groups as they carry out a speaking task, which normally requires each grouping to reach agreement before joining another group.

Example

In small groups, the learners have to agree on the most important of the five senses. They then join with another group and have to agree again, and so on, until the whole class is involved in one discussion.

In the classroom

Pyramid discussions are useful for practising a range of functions, including agreeing and disagreeing, negotiating, summarising, and putting forward an argument.

http://www.teachingenglish.org.uk/think/knowledge-wiki/pyramid-discussion