Can differentiate with double digits (double digit by double digit multiplication or even fractions). This site has great math projects. This can be done with nails in a board and colored yarn. Makes a great pricture too.
Thread the yarn through in a triangular pattern. (should be every fourth hole). I actually labeled the numbers on the dreamcatcher for my son so we could slip in a little number recognition. (Tip: Wrap a piece of masking tape around the end of the yarn