Every parent who does anything at our school has to do a Working with children check- even if its man a stall at the fete.
I agree with Ali- its very very hard to get a trained teachers aid even in a paid position- I have an untrained paid one 2 hours per week. It would be awesome to have one FT even untrained as they free up the teacher to help the rest of the class. I would be pleased if it was my child's class.