You say this because you don't know better, but its very common in schools for kids with learning or other disabilities to be in the same classes as other students - called 'mainstreaming' https://en.wikipedia.org/wiki/Mainstreaming_(education)

Teachers are 100% supposed to teach the standardized kids, the kids with disabilities, and the kids who are a little faster than everyone else. It's simply not possible to do with one standardized lecture without individual attention to those with special needs.

It's not some document, its literally a major movement decades old in education.