I've had a few queries so here goes..
I numbered the Jenga sets in their own plastic box with 1-6
in different colours on the box lid. I then numbered the Jenga blocks
1-48 with a felt tip the same colour as the box lid. eg Set 1 had 1
written in red on the lid and all the blocks were numbered 1-48 in red.
Pupils take it in turns to remove a block using one hand only and
answer the question of the number on the block. They then place the
block on top of the Jenga tower before play passes to the next person in
the group. If they can't answer it, they need to remove another block.
If they knock the tower over, have a forfeit ready like everyone else in
the group gets a sticker or they have to sing a song...
Hope this helps..