Scat by Carl Hiaasen

When Mrs Starch, the most feared biology teacher in Florida, goes missing during a school trip to the Black Vine Swamp, her class is secretly relieved. The school principal tries to cover it up as a 'family emergency', but Nick and Marta just aren't convinced. They think it's much more likely to have something to do with Smoke, the local troublemaker - whose run-ins with Mrs Starch are infamous - and decide to do some investigating of their own.