I had the same group as yesterday. They were working on factoring (trinomials). Some of them "got it" and finished things quickly. Some of them were still struggling with the concept. I helped those that I could.
One girl had a question. I helped her. She seemed to catch on. So, I moved on to walking the room and making sure that everyone was okay with the assignment.
A couple minutes later I passed the girl that I had helped. She was talking to her neighbor. She was explaining how to do the problem that I had just helped her with. She was explaining how to do it correctly. I walked on.
That's the greatest feeling--to know that the girl understood the concept well enough to explain it to a classmate. That's when I know I'm doing my job right.