My son did sets at the beginning of Grade 3.   Empty sets, subsets, adding sets.... etc.
I realize that EPGY is recommending getting 80% correct.  Having worked on it, I actually think that is too low, at least for my son.  At what seems to be an accurate placement, he scores about 90% overall.  Higher in some areas, lower in others.  To pass their final, you have to get 85%  (I think.  If not, 80%) .  The student effectively gets two chances at answering the question, so at the first attempt 80% makes sense.  But at the second time around, I think it needs to be higher.  On the calendar/sessions area, you can replay the sessions and see how what percent your child is getting on the first and second attempt.