We are 3D printing in our 6th grade classroom. I've seen more educational value in the actual CAD software (SelfCAD) than in the printer, itself. That's where it's at. We are applying the concepts of measurement, measurement conversion, volume, area, perimeter, planes, angles, flips, and an array of geometric concepts every time we design something. We had a bookshelf with a missing pin. On their own, my students took another pin, measured the specs, designed a new one and printed it to save the bookshelf. Truly amazing.