A townie or grocery getter type pannier is what I used while I was in school because I never found a good pannier that actually converted to a back pack that was comfortable and not ugly as sin. I just flopped my regular comfy backpack into the grocery pannier while I rode, then got to school and removed the back pack. I did what some of the other posters did by attaching the pannier more permanently so that I did not have to worry about it getting ripped off so much, zip ties are one way. Those townie and grocery panniers are pretty cheep anyways. Another way to go are the Wald rear baskets or the folding rear baskets by the same maker. They attach with bolts so are very safe! I think this is the best way to go for students who need to be able to carry a back pack on and off the bike.