Aristotle was a great taxonomist – he sought to put all phenomena into one group or another.  Ask a group or class to discuss an issue close to their hearts, for example – freedom, or the subjects taught in school.  Everyone in the room has to say something – but must begin what they say by using a word which begins successive letters of the alphabet.  All first words must have more than 3 letters – a word which has no role in the sentence prevents that person from completing what they wish to say.  For example, from a discussion about homework:

Child 1: Absolutely everyone in this room hates too much homework.

Child 2:  Besides me!

Child 3:  Children should decide for themselves what homework is set.

Child 4:  Don’t you think we would all choose what we can do?