A simple idea. You gain a passive bonus as you level, not even a whole percent per level but by the time you reach grand you have a 5 - 7% passive bonus to something.
Life - Outgoing healing. Ice - Damage on direct spells Fire - Damage on DoT's Death - Health drain Storm - Accuracy Myth - Minons are buffed Balance - Pick a school to get a passive defense against it. One school, can never, ever be changed.
As it stands you get a minor health and mana boost. All your stuff comes from your kit. Nothing really to show your learning your school better.