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.
Book art is a really bittersweet medium for me. I hate to see a book destroyed, on the other hand, the product of that destruction can be spectacular. ALSO - I miss the Minnesota Center for Book Arts and Coffee Gallery @ Open Book.