Teachers can print off a list of usernames and passwords for the students in their class. Go to the Admin page, scroll down to Student list and hit Download on the top right. This will download a csv version where you can then manipulate to suit you.
Note that any passwords that are displayed are temporary passwords. The student will be prompted to update their password when they first login. The 'Reset' button allows you to set a temporary password at any time, here is some more information on lost student passwords and usernames.