I believe the evidence claimed is that there aren’t better outcomes for smart kids. Schools that claim they have better outcomes just selected for kids that would always have better outcomes. Like if I claimed my basketball team has better outcomes because I got to make sure all my players were above 6 foot. These 6 foot players don’t necessarily benefit from being in a team with other 6 foot players, but I’m saying people should apply for my team because I’m doing so much better than the team that can’t make those weeding out decisions. I’m intentionally conflating the success of my capacity to select for success with my capacity to coach a team.