The current sign-in system can be confusing for 1st time users. It would be better if the sign-in interface offered more help and explanation, instead of relying on the teacher to explain everything. Some changes could include:
1) Give feedback if student tries to create an invalid password (too short, long, etc)
2) Could offer suggestions for ways to come up with memorable password.
3) The instuctions should reinforce the importance of memorizing your password.
4) When user has completed the 1st-time registration process, they should then immediately be prompted to confirm their new UserName or password by entering the data again. If they get it wrong the system could tell them what they should have put in (it could suggest the UserName + Password just registered). The student is not fully signed into the system for the first time until they register and successfully complete the confirmation screen.