Always during Catholic Schools Week there's a bulletin article about the Gladlyville Catholic high school. It always includes the students' average ACT score, with the suggestion that these higher-than-average scores are the result of the Catholic education.
Can we talk about that? There are two things that bother me here.
First: kids with more affluent, more educated parents score higher on the ACT. The discrepancies start early: they were more likely to receive good prenatal care, more likely to be born at full term, more likely to receive the neurodevelopmental advantages conferred by human milk, more likely to live in houses full of books and opportunities to be read to, more likely to be comfortable with the unspoken rules about how to behave in the classroom that can influence teacher-student relationships and student identity from the get-go.
Who sends their kids to Catholic high school? Parents who prize education, and parents who can afford the tuition. It may be true that your kids will learn things in a Catholic high school that will help them on the ACT. It is also true that many kids whose parents send them to Catholic high school are predisposed to score higher on the ACT. Although the bulletin articles suggest that the Catholic education drives the ACT scores, the actual causal relationships are more complicated.
Second: Catholic schools can't offer as much in the way of special ed services. Kids in the US are entitled to a free and appropriate public education. Private schools don't have to worry about the free part, and they also don't have to worry about the appropriate part: they can decline admission to a child who needs more supports than they can offer. Public school ACT scores include the kids with severe ADD, or the kids with low-normal cognitive skills who are hoping maybe they'll score high enough to get admitted to college, or the kids with ODD who bubble in the wrong answers deliberately.
If your fee structure means you're attracting kids more likely to score well, and you're not providing a suitable environment for the kids most likely to score poorly, maybe it's not actually newsworthy when your ACT scores are higher than average.
This XKCD is evergreen.