
No one, not even the system administrator, can look up a student or teacher's password. If a person forgets their password, the best anyone can do is to reset their password to its "default" or original value. As explained in Add a student, when a new user is added to the system, their password is the same as their username. The first time they login, they'll be forced to change their password.
Thus resetting a person's password amounts to setting the password to be the same as their username. The next time they login, they'll be required to select another password.
Clicking on the "Reset a person's password" link yields the form:

Select a person and click the button to get a confirmation page:

After clicking the "Reset Password" button, the user's password will be the same as their username.