If you are unable to open files created by students in newer versions of Apple Pages, Keynote or Numbers, have them follow this guide to save the files in version '09. (The example shown is for Pages, but the procedure is identical for Keynote and Numbers.)

Note there is also an option to save as Word (from Pages), PowerPoint (from Keynote) or Excel (from Numbers) to share documents with people who do not have access to these Mac-only programs.

(Unfortunately, there is now way with Garageband to save to the lower version.)