Summary
There is no limit as to how many teachers can be added

Vulnerability Details
this can lead to DoS in the loop iteration of the teachers which can eventually hinder the system operation due to high gas cost and even storage bloat since the contract is upgradeable or meant to be long-lived.
this can also drain the chool funds since too many teachers require a lot wages

Impact
the impact may be medium since it takes time fo the teachers to be added

Tools Used
manual review

Recommendations
impose a cap limit to the number of teachers to be added in the addTeacher()