Dave Caolo discusses the Guided Access feature in iOS 6:
Apple’s iOS 6 introduces a feature that will benefit teachers and parents alike. Guided Access is a new accessibility function on the iPhone and iPad that lets you disable certain controls within an app and prevents kids from navigating away. When I was a special ed. teacher, I would have loved something like this.
This is a simple but important addition. Caolo also notes other potential use cases, including locking students into an electronic exam or using the iPad as a kiosk.