Kiosk from the Chrome Web Store. The kiosk app is created by a company in Madison, Wisconsin called ZebraDog. They use the kiosk app to create eleborate design environments for Chrome OS.
One issue that I have run into with Chromebooks is the lack of a desireable start page for students. Often what the central office sees as a desirable start page is not student friendly, or narrow enough for a techer's desired use.
Kiosk is simple, the first time app is used you insert a url, and then everytime you use the app after that, it goes directly to that url in kiosk mode. If you need to change the url address, you will need to uninstall the app and install it again. It is important that what ever page you decide, you keep it self contained so students cannot venture outside the domain you select.