We don't allow students to change their password, instead we give them a 4 digit number.
If they forget it, they can ask their teacher who can click on a link on the desktop to get to the IT Faults and Resources system. On there they can log in to the user accounts section to browse for the student's name and password.
Any requests to change a password must be made through the IT Network department - I got sick of certain staff members changing passwords and not noting it down on the spreadsheet that used to be used