If you 'save' logins on your iPad from Safari sites, these logins are kept in the Safari settings on the iPad.
Go to Settings > Safari >Passwords & AutoFill >Saved Passwords. This screen will show all of the user names and the website that name is for. If you tap on the arrow next to the user name, the password is shown. If you have a passcode, it must be entered before the password is shown. Without a passcode, anyone could access the login information.
For teachers who have entered in incorrect username/password and this has been saved in the Autofill, you can delete the incorrect items in the Passwords & AutoFill. Tap on the Edit button in the upper right hand corner, tap on the username to delete and then tap on delete at the top left.