If you want to be talked out of it a couple of things to consider.
Is your time cheaper, when you consider building, updating, re/learning the tech to do it, fixing it when it breaks and the Liability for you and the school of data protection? When its compared to an off the shelf tool such as CPOMS or Evolve.
You get this working, 2/3 years down the line after staff are used to it, you win the lottery and decide to fall of the face of the earth. The school needs Data off it urgently for some sort of 999 level thing, but one of the weird sql calls you have to do to get it working fails for some reason, then what will the school do?