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.
*Even if your students are labeled "student" you likely STILL need to do this update due to the meta-data field.
NOTE: Users will need to hit the "refresh data" button after this update is performed.