The Lightning Thief by RIck Riordan

"Sir," I said, "where's Mrs. Dodds?"

He stared at me blankly. "Who?"

"The other chaperone. Mrs. Dodds. The pre-algebra teacher."

He frowned and sat forward, looking mildly concerned. "Percy, there is no Mrs. Dodds on this trip. As far as I know, there has never been a Mrs. Dodds at Yancy Academy. Are you feeling alright?" (15)

Twelve-year-old Percy Jackson has had some weird things happen to him before, as he has been to six schools in six years. But when his pre-algebra teacher attacks him while on a field trip, and then disappears with no one remembering her, that's just the start of Percy's adventure. Soon he finds himself be shipped away to summer camp for the offerspring of the Olympic gods and goddesses. But Percy seems to have discovered his new identity just in time, as he is sent on a quest for an item stolen by the gods. If you haven't started the series by Rick Riordan yet, now's the time to start with The Lightning Thief.

AMY