Thing is that even if You ride to school on a crappy bike someone can still take some bits off it that he might find useful. My mate is a bouncer and he locks his bike outside the club he works in. When he had to go inside as there were some problems with one guy someone nicked his qr`s.
I use my road bike to ride to work, gym and uni (if the weather is good) and taped all logos, plus have a big solid U-lock, very thick cable to catch both wheels, kryptonite saddle saver cable and an coil lock just in case. Tesco used to do a LOX chain (looked more like a motorcycle chain) for about £12-14 it looked solid and was very heavy, long enough to catch both wheels. My mate used to leave it at work so that he wouldn't have to carry it and then just lock the bike once he's there. Must have been a good chain as he gave it to a friend to lock his scooter in Pilton area of Edinburgh and no one nicked it 🙂
Worst thing is that even if they will not manage to nick it they can give it a kicking, slash the tyres etc so if they can't have it, neither will You.