My students struggle with number sense as we expand to larger numbers. I have found that by having them focus on puzzles of hundreds boards, they make the connections between numbers (1 more, 1 less, 10 more, 10 less) on their on in a more concrete way.
I cut the puzzles into varying numbers of pieces and with increasing shape difficulty. I then laminate the pieces and put each puzzles in its own bag or envelope.
My kids love to do these - they do not even realize they are learning!