You have a gift for casting spells from a certain school. Although your spells from this school are more potent than those of other casters, you are not as effective at casting spells from other schools.
Choose a school of magic. Add 1 to your caster level when casting spells from that school.
Reduce your caster level by 1 whenever you cast a spell that is not from your chosen school.
Characters with this trait might be loudly vocal about the merits of the school of magic that they understand most readily, or they might feel awkward and out of place around "normal" spellcasters as a result of their unusual aptitude.