Needs review
Source: Player's Handbook

Description: Choose a school of magic, such as illusion. Your spells of that school are more potent than normal.

Prerequisites:

Required for: Greater Spell Focus, Spell Mimicry

Add +1 to the Difficulty Class for all saving throws against spells from the school of magic you select.

Special

You can gain this feat multiple times. Its effects do not stack. Each time you take the feat, it applies to a new school of magic.