Like several commenters pointed out, using separate systems seems the best approach for the short term. I suggest that you first implement the system for multi

Like several commenters pointed out, using separate systems seems the best approach for the short term. I suggest that you first implement the system for multiple schools before re-architecting your system. Your will have better understanding about which parts of the system should be customizable and which ones should not. Do not attempt to make your system overly customizable. I have seen several systems where almost everything could be customized. In most cases these were pretty complicated to use, and of when the customer came with some request we had to change the customization code itself, because the request could not be satisfied with a change in customization parameters.