The rule of thumb is: NEVER share a login access with anyone. If someone is supposed to have access, s/he will be granted access by the powers-that-be.
Many institutions track who is accessing their systems. This may include the login credentials (userid/pwd), as well as IP address and information about the device, operating system, etc.
Some institutions specifically prohibit sharing access. Signing on using another's credentials may be considered illegal access, hacking, breach of system security. It may also be considered "impersonating".
Parental access and case manager access may differ. For example, a case manager may have read/write permissions and be required to enter a log or evaluation of student progress. Meanwhile a parent may have "read" permissions only, in order to view what has been posted.
To manage expectations going forward, you and your child, the student, may wish to have a conversation and decide together whether either of you will ask the case manager what s/he has access to, for what time period, what the case manager's role is, etc.
