Most “Christian” schools in the south were founded by wealthy whites to keep their kids away from black.
I know most of my aunts/uncles were sent to one for that exact reason when schools were forced to integrate. Even while the school was 30-40 minutes away.
As the article said, they are usually worse than public schools. I got a much better education at a public school then when I was at a private “Christian” one, which is saying a lot for the rural south.
In decently sized metros, wealthy whites could already send their kids to the "old line" private schools in the area.
In those metros, the post-1960s schools that popped up tend to be of lower quality and some of them only managed to stay open for a few years, either because they could never achieve financial solvency or the families who had been attending them simply White Flighted themselves out to new suburbs and exurbs and enrolled in those public schools, obviating the need for the segregation academy.
Some of these schools were literally some mothers teaching kids out of some spare rooms at the Southern Baptist church. No specialized instruction, no varsity sports, no science labs or fine arts. These people were so unhingedly racist that they would rather deprive their children of all those things than have them have to share them with Those People's children.