These can be laminated to be used with a dry erase maker. I find especially for beginners learning how to borrow and carry over having the actual physical boxes to regroup and "hold" the numbers is an effective way to increase student confidence.
Students can use these mats to answer questions from their worksheets that do not have boxes on them. I have found that that students remember to show and do the work in each step allowing them to keep tracking of their number regroupings much more effectively.
I have found this to be particularly useful for students still learning to grasp these new concepts or seem to be weak in their understanding of borrowing and carrying "1" group of ten or more.