Alanna: The First Adventure, by Tamora Pierce, is the first installment in the Song of the Lioness quartet. The heroine of the story, Alanna, is to be sent to a convent to study magic, while her twin brother, Thom, is to go to the palace to train as a knight. It isn't a good match; while both twins have what is known as "the Gift", Alanna is much braver and more skilled at fighting than Thom, while Thom has more of a knack for magic. So they decide to switch places. Alanna, disguised as a boy, heads to King Roald's palace to begin her training, and Thom, disguised as a girl, heads to the convent.
Once she arrives, Alanna discovers that being a knight isn't all about battles and glory. She must also learn to work hard and curb her fierce temper before it gets her into trouble. Throughout the course of her training as a page, Alanna will make more than one enemy...but she will also discover a host of unlikely allies.
This was overall a very good book, although it wasn't as good as some of the other Tamora Pierce novels I've read. It seemed as if most of the action took place at the very end. However, it was still enjoyable, and the heroine was funny and likable. But I'd recommend reading some of her other, better books first.