Earlier quoted context omitted.
> Private school teachers get paid less than public but produce better outcomes. I'd like a citation for that. I can't help but imagine that private schools game the numbers, because when I worked for a school district that's what I saw: private schools can easily get rid of underperforming students and pretty much never take any with disabilities.
The most recent NAEP data shows what other research has found: Private school students score better in almost all subjects. https://www.nationsreportcard.gov/dashboards/schools_dashboa... On college entry tests such as the SAT, NAIS found that students in private schools consistently out-performed their public school peers in all subject areas. https://www.nais.org/magazine/independent-school/spring-2016...
His doubt is that private teachers that are paid less than public school teachers provide better results. To prove the original assertion you need to include the income levels of these private school teachers and graph them against the performance and income level of the public school teachers.