yes, the marginal utility of the "better" education is not generally worth the tens of thousands of extra dollars, whether it be novel instructional methods, extra time/attention, better credentials, or nicer, more advanced facilities.
but like most such situations, i suspect wealthy families are not simply buying better instruction, but rather exclusivity and esteem. the treadmill they're on is an attempt to maintain and improve their (apparent) social status.
money doesn't buy you a ticket off the treadmill. even the richest people jockey with each other for status. jumping off the treadmill means social isolation and most folks can't stand that.
It is more that they're buying their kids a social circle that includes the kids of other elite families. They're not buying better math instruction, they're buying access.
It's not just that it's not worth it, but that growing up in the rich-private-school/elite-suburban-school bubble is actively detrimental to people down the road. It's making the kids less happy and less able to be a part of the real world.
but like most such situations, i suspect wealthy families are not simply buying better instruction, but rather exclusivity and esteem. the treadmill they're on is an attempt to maintain and improve their (apparent) social status.
money doesn't buy you a ticket off the treadmill. even the richest people jockey with each other for status. jumping off the treadmill means social isolation and most folks can't stand that.