Primary teachers and co-teachers can remove a student or co-teacher from a class at any time.
Removing a student from your class removes their grades from the gradebook and they won't see your assignments in Classroom. However, their work remains in the class folder in Google Drive and their posts remain in the class stream.
Go to classroom.google.com and Sign In.
Click the class > People.
Check the box next to the students you want to remove.
At the top, click Actions > Remove.
Click Remove to confirm.