Are poor kids more likely to be on IEP’s?

Hi- I’m a substitute teacher who is just trying to make sense of the different classroom environments I encounter. I’ve worked in several different schools but obviously have not done a research study on this topic. It was shocking to me that in poorer neighborhoods, I’d encounter gen ed classrooms where more than half the class was on an IEP or 504. In wealthier neighborhoods, there were not nearly that many kids receiving special ed support. Is this just a sampling error, or is this a common occurrence in public schools?

Edit: thank you for all of your insightful replies! You’ve helped me understand this complicated issue better today.