You, as a teacher, have the option to change a student's name on your dashboard to make your life easier.
1. Click on the Actions button in the preview of the student you want to edit the display name of.
2. Select Edit name.
3. Change the display name to one that is easier to identify for you.
4. Press Enter.
Note that this will only change the way the student is displayed on your teacher's dashboard, the actual username and the way the student appears, for example, in the global leaderboards will still be the student's actual username.