What do I do with the child that tantrums during transition?

First we need to identify the ABC’s.

Antecedent

Behavior

Consequence

A: what happens before the behavior is occurring; environmental variables? interactions with adults or peers?  hungry? tired? wanted an item that was denied or in possession of another?

B: what does the behavior look like?  describe it so that all who observe ‘know’ that is the behavior you are targeting

C: what comes after the behavior; time out?  extra homework?  reprimand from adult? laughing from peers?  What is the consequence that is maintaining this behavior?