A new Harvard Business School case study of the Success Academy charter network offers valuable insight into why its schools are so, well . . . successful. New York officials should read every last word.

The study recounts some of the network’s history: These last two decades, New York City public schools were among the nation’s “lowest performing but highest funded” and, despite still more funding from Mayor Bill de Blasio, “there was scant evidence of improvement at underperforming schools.” (Massive COVID aid from DC has bloated spending even more, and Gov. Kathy Hochul is now pumping in boatloads of added cash on top of that, even as enrollment has plummeted.)

The paper describes how Success founder Eva Moskowitz, as chairman of the City Council’s Education Committee until 2005, had pored over school-union contracts: “No rational person,” says Moskowitz, could read the union agreements “and say, ‘This is the best for kids and learning.’” They were designed “completely for adult interests.”

So in 2005, Moskowitz “set out to prove what was possible.” Over the next 15 years, despite opposition from unions, she opened 47 charter schools (publicly funded, privately run schools open to all kids, free).

“With a student body comprised almost entirely of students from low-socioeconomic households, Success Academy Charter Schools had achieved extraordinary outcomes, with superior test scores and college placement results,” the report notes.

Most remarkably, these schools erased the “achievement gap” that plagues regular public schools: Success kids almost invariably scored at the highest levels, regardless of family income or racial background.

Last year, amid COVID, SA saw 100% of its seniors accepted to college. As with earlier Success classes, students got into top schools — Columbia, Yale, University of Pennsylvania, University of Chicago. Compare that to just 30% enrollment in bachelor’s programs among minority and low-income students in the city-run school system.

Parents noticed: Families “in neighborhoods with low-performing district schools were applying in droves. The ratio of applicants to available seats averaged 6 to 1, with more than 90% of eligible students applying in some areas.”

The paper also notes SA’s secret sauce: enormous attention to detail. Careful design of classrooms. More training for staff. A well-constructed, challenging curriculum. Close ties with parents.

Another key factor (though the study doesn’t talk about it much): the lack of union and Board of Education mandates. Success teachers aren’t unionized, and Moskowitz, well-versed in the workings of public-school bureaucracy, knew what to avoid.

Alas, despite the fierce demand for SA seats, the school can no longer expand because lawmakers capped the number of charters in the city.

Educrats can certainly learn valuable lessons about how to run great schools from HBS’s study. But if Gotham wants to broaden opportunity fast for desperate kids, it can simply lift the cap on charters and let schools like Success work their magic.