While security is key, in classrooms where teachers move between classrooms, the full username/email and password sign in every time a user switches to a new hour detracts from time spent preparing for class.

An easy solution is to hold the persons username/email in a queue on the left side of the board (similar to what Chrome does with multiple users) and then have teachers JUST type the password. This provides a nice balance of security and ease-of-use.

Watching teachers log in several times a day in front of high school students is painful. This might be a quick solution for them.