Thinking Blocks

I have been using Thinking Blocks for several years with students who are working ahead of their peers in class.  It allows students to use blocks to model word problems.  Because the site includes all four operations, I think that it would be a great resource for reinforcement as well as for enrichment.  It easily allows for independent learning as it has videos that introduce each topic and an easy way to track progress.  There is even a printable certificate once a level is completed.