Sorry - only just come back on:
I'm only speculating, and obviously don't know in these circumstances.
But if there is a child who has poor behaviour, or difficulty controlling temper, it is just possible they might be paired with a well behaved child, in the hope the 'good' child will model an example of better behaviour.
It can often happen in class, when an over-chatty child is put next to a very quiet one, who will normally ignore the chatty one. (Children often don't like it though, and the 'good' one says she can't concentrate!)
But, as I said I think you are entitled for a proper explanation from someone with responsibility for the pairing.
"Transition" presumably means the transfer to secondary school. These days, that is usually handled sympathetically, with Yr6 children getting a couple of days practice-run in the secondary school, probably meeting some of the teachers they will have, and seeing some of the classrooms. Yr6 children are invariably worried about the size of a secondary school, and fear they will "get lost".
Are these the only two children involved in this Drama Therapy? I hope I haven't worried you unduly.