Group Work Doldrums

Today I put kids in groups by ability. This means I put all the kids who really get the topic in one group, and gave them harder work, put all the kids who don't get the topic in another group and gave them basic work. You're thinking "but won't that just give the other kids an excuse to keep on not doing the work that they have been not doing?" And in some sense you're right. About half the kids who are the "don't call us slow" group did not do anything, but the other half came face to face with what they did not know and took a few steps forward kind of like a kid taking their medicine. The kids who did know what they were doing were really busy working furiously on their work because they were glad to be getting a challenge finally. If I am to do this again in the future I need to EXTRA scaffold the stuff for the "we don't have any smart kids in our group" group, so that they can dive into it, and maybe put them in the same part of the room so that I can circulate more with them, as they need more direction. I also need to not put all the kids who have not done anything for the last month together, or near each other, then it just causes them to want to do nothing and bother the people in other groups.