Google isn't one to take initiative when it comes to updating the Chromebooks, typically they must be updated by hand. Students don't have access to settings in the Chrome browser, but they should be able to access what they need to update from the control panel.
1. Click the clock on the taskbar.
2. Click the settings gear.
3.Click on "About Chrome OS
4. Check version.
5. Click to update.
When it's done it will ask you to reboot.