Thinking Blocks is a series of free iPad apps based on the web tool of the same name. The apps are designed to help students develop models of word problems. In each of the apps students create block models to work through a series of progressively more difficult word problems. As students work through the problems they are provided with feedback as to whether or not they are using the correct sequence to solve each problem. There are templates and problems for addition, subtraction, multiplication, division, fractions, and ratios. You can find links to all of the apps on the Thinking Blocks site.