The Chromebook's have keyboard settings under Settings > Device > Keyboard that the students commonly mess with. The common things we see changed are the mappings of common keys like Shift, Backspace and Search, as well as the repeat rate of keys (how fast they type multiple keys if you hold a key down). If you follow the above path to find the settings, this is what that page looks like and what the settings should be by default:

As always, if you're having troubles with these directions, please feel free to reach out to us.