Pinshape has just released a design contest that will last until October 15th. For any teachers out there, this looks like it may be a great class project. It incorporates aspects of both designing with given constraints, while also giving a very large degree of artistic freedom as well. Depending on the workload desired it could serve as either a team project or an individual project as there are several separate parts to be designed.
Design contests like this are common on a variety of websites that have 3D models. Most of these design contests provide fun and exciting ways to get people printing and innovating in ways they may have not have previously thought to. Even if this challenge isn’t quite the right fit for your class, the template should carry over to a variety of other subjects by simply starting off with a core piece and encouraging creative solutions to whatever problem you have.