Usecubes is a website and iOS app that allows the user to create 3D models out of blocks.
What is really cool is that after the model is created, it can be ordered as a kit or downloaded for 3-D printing. The kit looks like a specialized Lego bricks kit, but made up of the 3-D model that was designed in the app. If you run the app under iOS, you then have the option to download the model for 3-D printing (I don’t know what this isn’t included in the web version, probably a price thing).
Usecubes is an easy introduction to 3-D modeling that students and teachers should be able to use pretty quickly.