And you cannot raise your Destruction skill by blasting the targets with fire (darnitall) but the remaining schools have spells you can spam-cast to raise your skills (summon bound dagger for conjuring for instance).
You can make a fire,or some other kind of,damge self to train destruction.
Also for the OP if you get the fighters stronghold DLC there is a combat trainer you can buy that you can spar with as much as you want.It's a good way to train a combat skill or blocking and also learn some strategies against differant types of blades.
The DLC is available through xbox live and doesn't cost that many microsoft points,I think around 400 but I'm not sure.