How can I find out SES and race demographics for a given school district?

If you are looking at a particular school, go to that webpage. If you're looking at the ISD, and the info is not there, there is a contact number. When all else fails, call the school or district info officer and get them to walk you through it. They can probably direct you to the info on their site. They will be glad to help and the info you seek is public information that must be provided upon request. Sometimes websites are so obtrusive that you need help navigating them.