post #21 of 21
DD is doing these "enrichment math" worksheets in school--they vary somewhat in difficulty, but she finds them a challenge. Plus, you can print them for free. However, they only go up to 5th grade so may be too easy. They are more along the lines of brainteasers and logic problems a lot of the time.

http://www.sbac.edu/~chiles/media/mediasunmath.htm