As a product of 13 years of private education, I think they're totally worth the money. Here's why:

The class sized were extremely small. I had, on average in high school, a 7 or 8 to 1 student-teacher ratio. Imagine trying to daydream or pass notes with only 7 other kids in your class. Not going to happen.

We learned how to shut the hell up. The fear of a ruler on the knuckles is enough to make you stay in your seat and pay attention to the lesson.

No bullies. Seriously. No lunch money bandits, nobody pushing you around, smacking your books to the ground. Not even any real name calling. The overweight kids got picked last for kickball, but no one ever made fun of them for it.

More parental involvement. I've seen a bunch of studies that show that the more parents are involved in their kid's education, the better they do. If a parent is dropping between 5-25k per year, you better believe they're going to make sure they're getting their money's worth.

Everyone else is right: if the kid has some kind of learning or emotional disorder that would require extra help, public schools are probably the way to go. But if the kid is at least an average student and would benefit from tougher academic competition and a stronger sense of community, then you can't beat a private education, especially in the k-8 years.