Panniers are the way to go here. They will change the handling a bit, but since the weight is near the axle stability is good. When I commuted, I carried up to 40 lbs that way, distributing the weight on each side. I used
Banjo Brothers saddle bags, that allowed me to quickly remove and carry.
Here's another option to consider: Assuming that most of the weight is textbooks, buy used copies of those books that you can keep at home. That way you reduce the back and forth load. We did that for my youngest daughter and it worked great. Most of the textbooks are common and can be found cheaply on eBay etc. Just make sure that you get the right edition.
Good luck