The attempt to prove that public schools are just as good educationally as are non-public schools reminds me of the attempt to prove that bumblebees can’t fly. Are you going to believe the calculations or your own lying eyes?
If public schools are just as good, why do poor families in cities like New York spend money to send their children to parochial schools?
The researchers “adjusted” the data for various factors relating to student background. Maybe they should also adjust it to take into account the superior discipline found in non-public schools.