How to turn on Single App Mode in iOS 6
Single app mode allows for teachers or parents to lock down their iPhone, iPad or iPod so that students or children cannot wonder to different apps and "forces" them stay on task.
Setttings ----> General ----> Accessibility ----> Guided Access ----> ON
"Guided Access keeps the iPhone on a single app, and allows you to control which features are available. To start Guided Access, triple- click the Home button in the app you want to use."