The other week I had to sub in special education for a few days. The children had been learning borrowing and regrouping for months but hadn't been able to catch on to how to do it. Two of the children had been in life skills until just this past year so that may have been part of their difficulty. They would either just randomly write another number on top or would reverse the problem (5-7=2) Because of schedule changes, I ended up only have two of the students most of the time. I showed those two how I borrowed and regrouped, by having them just write a 1 next to the number on the right side instead of trying to convince them to add 10. And they got it. After they had done that a few times, they were able to cross out the number and write the correct number to add on top. Those two continued to borrow and regroup correctly throughout the week so there is a good chance they will continue to do so this week too. The real interesting thing is that their teacher would have never shown them this because she wanted them to always cross out the number so she could be sure of which number they were working with.