Source: Digital Design Platform for Education | InVision

InVision provides prototyping services for applications, students can use the website to collaborate on mobile apps and get an idea how the app would work.

This would be geared toward the higher grade levels, especially students who may be interested in a user interface or programming career. The interface may be a little advanced for use at the younger age levels.

Pretty nifty site, and anyone can have one project on it for free.