Apple does an exceptional job at making devices easier for people with disabilities. In addition to Accessibility features like VoiceOver and Zoom, Apple has now added Guided Access to the iPad with iOS 6.
Guided Access limits an iPad to just one app, allowing young children or students with disabilities such as autism to remain focused on the content. The new feature disables the home button and can restrict touch input to certain areas of the screen or altogether.
Once Guided Access is on, you can open the app you want to restrict and triple click the home button to activate the single app mode.
You should get a screen similar to the photo on the right. From here you have a few options. You can restrict certain areas of the screen by drawing a circle, square or triangle with your finger. You can then adjust the size of restricted area and move the placement. You can also turn off all touch input and any motion detection at the bottom of the screen. Tap Start at the top right of the screen to enter Guided Access.
To exit from Guided Access, triple click the Home button and enter the Passcode you set earlier.
There you have it. A very simple, but useful feature if needed.