It's a two-step backsave.
Step 1 -- backsave in CC 2014 to CC 2012, and open in CC 2012
Step 2 -- backsave in CC 2012 to CS6
Know that NONE of the features exclusive to the more recent version will be backsaved into the earlier version.
If the school is renting Creative Cloud, it has access to, can download and install the 2012 version. But will it? Ah, there's the rub.......