It sort of is already. The segregation of Americans by school district based on what their property taxes are already accomplishes this. Observe the standards to which schools that are wealthier (because of better taxes) vs schools in areas with lower taxes. The parents of the kids in the former are expected to play a more imperative role, the kids are challenged a LOT more. My fourth grader was expected to do at least 3 detailed book reports, each book at least 200 pages per book, including learning to present her findings in a timed manner. They were graded informally on a detailed rubric. They advance kids to higher math grades based on the child’s skill level. So there are 4th graders doing 5th and some exceptional ones 6th grade math.
This contrasts with another school district we were in earlier. Very loving teachers. But they had no space to challenge the kids. Because the teachers had to own the responsibility of getting each kid across the finish line for the grade.