The good news is that the skills you have picked up using your schools CAD system are transferable to OnShape, i was quite surprised at how familiar it all felt, you can also import your existing Solidworks and Inventor drawings and models into Onshape and it will export in many different formats including STL, please take a look at OnShape as a possible alternative to your schools CAD system.
OnShape are running some short online webinars that you might find interesting, click on the following link if you are interested in registering for any of the upcoming events https://www.onshape.com/onshape-sketch-aug-11
Happy CADing!