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.
This could be a fun way to create Calder acrobats! Swing From An Empty Shoe Box Project For Kids - by Krokotak - == - By Russian educative website Krokotak, here is a cool project for kids, with a tutorial full of photos that dispenses words.