Sometimes parents make a mistake and create their parent username as the students username. (In the old system, there were no parent accounts, so it's possible it was brought over this way.)
1. Search for the parent
2. Click on their username
3. Go to username and change it to what the parent would like.
4. You may now need to go to the student account to change that one as well. If so, search for the current student username and follow the same directions.