Hello Jessica,
What a shame they threw both groups together as you could have done something of outstandingly high quality with two groups of ten.
Still there's always a way to make things work!
The great thing about using plays is that the better students get longer roles while the less able say less, but they still learn through listening and participating in the group.
I have thirty
ESL role-plays and skits which are simple and great fun - however I usually recommend groups of up to fifteen kids at a time in order to avoid making rehearsals a drag.
However to get around this pupils can be grouped so that two or three children have a line that they say together, which minimises waiting time in between having something to say.
The best thing is to check out the free skit from the plays page to check the level. It's deliberately simple and repetitive and they ALL are. I have put these on with children aged 4 to 12. The twelve year olds can usually lean a skit per lesson while the 4 year olds can take up to 7 lessons to get it together.
However let me add that with the four year olds I don't spend the complete lesson on the skit - we do about 10 to 15 minutes on it, that keeps it fresh and the next lesson we bring it out again and add to it.
I do everything by listening and speaking only - the kids never see the script - though one could use the script once it has been learned usefully for writing and spelling activities.
Here are a couple of helpful posts:
Preparing short plays in English
And, for larger groups:
Plays at middle school
Kind regards
Shelley