If the user account username has been forgotten, the student (or parent) should contact their studio and ask them to look under the user tab of their profile. The username will be displayed there.
Most of the time, the username will not be your email unless you specifically set it up that way.
Please note that usernames are case-sensitive so they must be typed exactly as they appear in the system. If the username looks like it's exact, double check that a space wasn't added after the username.
If there is no User tab under the student's profile, a user account has not yet been set up.