Can I reference another essay in the one I'm writing?

So basically, I’m applying for a college on the common app. My common app essays has a back story that I want to reference in a smaller essay that I’m writing for a school. Should I do this or will the admission counselor just get confused?

I wouldn’t. Each essay - other than perhaps the additional information section which you can use to clarify something that you’ve mentioned in the CA essay - should stand alone.