I’ve always used the free desktop version of SketchUp for my students to create 3d models for printing, however we have been forced to go to the Free version of Sketchup Online for schools. I am having trouble accessing the files the kids share with me and, I’m unsure of how to import a shared file to prepare it for printing.
Where are you having them save the files? Assuming you have access to that folder via your computer, you should be able to click on the file folder icon in SketchUp and choose Insert>Your Computer. Navigate to the folder and select the file.