An Echo Administrator must perform this action.
A change was made to school browser to only show users who were designated as students (meta-EchoUserType = "Student") to eliminate test accounts and the cases where teachers were enrolled in PD. As long as any new student accounts are properly labeled a "Student", they will show up in the school browser.
In most cases you need to update your user information, the below link will tell your Echo Admin how to accomplish this.
NOTE: Users will need to hit the "refresh data" button after this update is performed.