Once a month is a very looong time specially for a school with kids having less information about what is secured and what is insecured. Weekly looks more promising..
Why does SEP detect a file but is not able to delete or Quarantine it ?
Ans :These threats they hook themselves either to explorer.exe or any running process and sep cannot delete or kill the process at it will have to kill explorer.exe as well..
Sometimes they install themselves as a service and is set to automatic ..so sep is not able to take any action as the service needs to be halted.
For these reason SEP requires a reboot to take the action.
Using any third party tool eg Malware Bytes will always solve the problem temporarity.
But what if the same virus is there on 10 or 100 computer at the same time..
or everydays you find a computer getting infected with a threat that previously you had cleaned using MBAM. Having definitions for them will be benificial for you as well as millions of people who are using SEP and might get infected with same threat.