Confused about Transfer Essay

I am looking to transfer for the 2017-18 academic year but am a little confused about the essay. I have already composed it and put it onto the common app, but certain sources say it should be school specific. I am not sure how I am supposed to do this when I am going to apply to four schools and the common app essay is meant for all schools. I know that some schools have the supplement that explains why you want to go there so I’d think that would be the proper place for me to explain why I’d like to transfer to the specific school. Any ideas or advice?

The commonapp will go to all schools. Therefore, you can’t really make it school specific. The schools that care about having a “why us” essay will have a supplement. For my transfer applications, only about half of them have supplements. Most of the schools that don’t, have higher admittance rates.