This app is basically identical to this publisher's other app titled "Addition !" Both apps are ok if the goal is to have a student practice the addition and subtraction algorithms repeatedly in a rote fashion (a practice that does have its place), but it doesn't seem worthwhile to speind $2.99 per app on these when similar tools are available for free as Java and Flash applications on the internet. There are no conceptual supports here other than algorithmic steps that the app provides if the "help" or "hint" buttons are pressed. The app could be improved if an option were added to show how a model such as base ten blocks coincides with the numerical manipulations for a given subtraction problem. Such a change would provide a conceptual support for the algorithm, and also make this app "feel" more like an application that takes advantage of the affordances of technology. Again, as the app currently stands, it doesn't feel much different than the worksheets I used to plow my way through as an elementary student in the '80s.