"Japanese Erasers" have been very popular with kids for a several years, as have keychains that hang in bunches on the outside of backpacks. I find both, though the erasers in particular, to be excellent 3D learning tools. When taken apart they're reduced to basic 3D shapes that can be modeled on the computer then reconstructed as 3D printed objects, which are wonderful keepsakes of their introductory modeling class. I also consider joinery to be an important early skill for young inventors to develop. So the most interesting designs in my class are those that consist of multiple pieces that are interesting whether together or as a pile of printed parts. The creation of this simple object, together with others that I've uploaded to Thingiverse, are useful exercises for anybody learning 3D modeling.

• Bob Krause
  Inventor Studios
  Berkeley, CA
  my first name at inventorstudios dot com