Each course gradebook is automatically populated with the correct roster of students based on the data imported from your school's student information system. As students add, drop or change periods, your gradebook is automatically updated after each of the nightly imports.
This article briefs on how can you prevent schedule changes in the student information system for the next term from showing up in School Loop too soon.
District Admin can block imports while schedule changes are being made, or contact School Loop Help Center and they can block/ unblock imports for you. Just be sure that imports are unblocked the day before the first day of your new term, to ensure the new schedules get imported.