Fully 50% of the table is useless, and has been since the introduction of the metric system in 1970.
So only do 2-9 x 2-9. That's 64 facts to memorize.
First get them to write it out by addition. If they can't do this then you may want to work on addition instead!
Everyone stands in a ring. The teacher's current favourite starts. Their job is to ask their fellows questions they can't answer.
The current favourite starts. He should pick someone. It's ok to pick on the weakest! Ask them a question. If they can't do it, you get another go. If they can, then they become 'it' and it's their turn to persecute.
I'd imagine that after half an hour of this, your whole group will be table perfect.