Take to the Skies — R.T. Martin

Cassie wakes up on her sixteenth birthday only to realize she's been floating in her sleep. With her brother's help, Cassie learns how to control her new flying power, but she's afraid people will think differently of her if they find out. She's willing to do anything to keep her secret -- practicing in the middle of the night, lying to her parents, even blowing off friends. But when a friend is in danger, Cassie must decide whether or not to help, even if taking action means revealing her secret.