After students graduate they may continue to need access to login. This article explains what happens to a student's access once they are graduated.
Student logins will continue to work after graduation. Their role will change to Alumni/Alumnae and they will be given Alumni/Alumnae access. If a student is withdrawn, access can be removed for both the student and his/her parents/guardians which this goes over https://www.blackbaud.com/files/support/howto/coveo/k12/bb-core-access.html.