My third graders just cannot grasp this. When we work in small groups or whole class they seem to do fine (unless they're really fooling me!), but they just took a test on this concept and bombed it. I feel like all the work we've done with it was worthless. When they have to regroup once (two-digit regrouping) they do perfectly fine. It's when we get into the hundreds. That's when it becomes a problem. Does anyone have any neat little tricks or ways to help the kids remember that they might have to regroup in the tens place twice sometimes?