My DD10 subject accelerated in math from 1st to 3rd. We had her do a 2nd grade math workbook over the summer so that she wouldn't feel like she missed anything. One problem, the workbook was traditional column addition and subtraction and her school uses Investigations. She kept getting told that she was doing it "wrong." She could look at the problem and write the answer. She kept getting marked wrong because she wasn't drawing sticks and dots. She was convinced until last year (4th grade doing 5th/6th math) that she wasn't as good at subtraction because she skipped 2nd grade math. If anything, her "gap" has been psychological. My lesson learned: if you try to fill in the gap with workbooks, etc., try to make it compatible with the curriculum.
