Well you peaked my curiosity so tried it:
Took a 2.5 course backup and attempted to restore to a 2.4.4
When arriving at the last step (6. Process), this warning was shown
This backup file has been created with Moodle 2.5 (Build: 20130514) (2013051400) and it's newer than your currently installed Moodle 2.4.4 (Build: 20130513) (2012120304). This could cause some inconsistencies because backwards compatibility of backup files cannot be guaranteed.
It did restore without further complaints/warnings. For the most part, links to files like PDF's and a Captivate movie or two worked - those were locally uploaded/stored files. There were no add-on/plugin activites or blocks used in the course.
So, even though not recommended, it *might* work ... but, by the time you get around to trying it, things could change. Another item to consider ... schools sometimes are a little shy about the size of files one can upload to the server. If you develop like crazy and go nuts with all sorts of files/movies/audio files, etc., your backup might be over the limits of what the school will allow. So think I'd ask what that limit is/will be before hand. If you do have to break up a single course into 2, one can restore a course and merge it into an existing course in 2.4.x (although I did NOT try that with a 2.5 backup to a 2.4).
Uhhh ... wouldn't make this a habit moving forward. Consider your local instance like a sandbox to the server version and from this point forward, match versions. Your school might upgrade to 2.5 in sort order, however. ;)
Best of luck! 'spirit of sharing', Ken