Tony Vincent posted these instructions for forcing the use of a single app in the educational (or home) environments with iOS 6, which was released today. Read his article here.
This is a wonderful addition, particularly for using iPads in music education.
Imagine this: you have four iPads that you can use with your students, which you wish to load with a PDF Music Reader, as well as to link audio files within that app, so that your students can do sectionals. How do you make sure that your students stay on task and in the app you want them to stay in? Guided Access.
This would also be ideal so that you could use the iPad in testing.