While this may not be relevant for the upper grade levels, here is a technique you should try if your child has problems with addition or subtraction. I have used this technique quite successfully with children in these grade levels who are having problems learning how to add or subtract whether the numbers are 3 or more digits long or not. Let's use an example. The child is given the following problem 365 + 447. First step each row is separated from each other. Second step use cards or crayons to show the answer. 7 cards + 5 cards equals 12 cards. Next repeat the same process using 6+4+1 equals 11. Explain to the child that you add the one from the previous 12 because it is left over from the previous row. Kind of like having a meatloaf sandwich, the day after you have had meatloaf for dinner in order to get rid of it. Then you do the final row 3+4+1=8. This will give you the grand total of 812 as the final total. Through both seeing the results through the cards and going through the process step by step, the children get it. I taught kindergartners to do nine digit math problems like this and it is good for all learning types. Try it and see for yourself.