The Song of the Lioness Boxed Set by Tamora Pierce

Alanna want's to be a knight more than anything in the world, but girls aren't allowed to be knights where Alanna lives so she switches places with her twin brother and pretends to be a boy. She then goes off to knight school where she makes some friends and enemies and learns how to be a knight.

Alanna's a pretty strong heroine. She stands up to whatever or whoever her adversary may be with all that she is and doesn't let anything stand in the way of what she wants, which is to be a knight. She does go through some tough times though. She doesn't rely on anyone for fear they might think that she's weak and she does doubt herself quite a bit, but I guess that makes her a bit more realistic. Overall a pretty good series.

The books in order are; Alanna, Hand of the Goddess, Woman Who Rides Like a Man, and Lioness Rampant