I group multiple ways. (6th grade)
Math with Teacher- this is the lesson. I have 1 group that gets it the first time, one that has to hear it twice, and the third I have to simplify everything and they might get it the fourth time.
Math by Self- independent work, this is the stuff that I grade. It may also be timed drills, which I don't grade but monitor progress.
Math with partner/group: these are games or problem solving activities. I make the groups hi/lo so that the lower ones can work with and see how that higher one works problems. 2 students have told me that they finally understood a concept after their partner explained it to them.