The intent that the school was founded on is entirely divorced from its role as an elite feeder school. SFS and Dalton share in the class demographics of their respective schools, their usage by high-earning parents, and how they're reflected in their alumni network.Sidwell and Quaker values are a part of regular life for most of their alumni. And the larger community never goes away. I still attend meetings for worship. So even if the school has become a place for the wealthy elite, the intent that the school was founded with carries on. The author of this article is out of touch if they are lumping SFS in with Dalton.
The real question is why is the public school experience so lacking and why aren’t there more private schools for parents who care about the quality of their kids educations?
Public school is "lacking" because of a feedback loop of austerity measures, underpaid teachers, difficulty in producing a uniform, yet flexible education, and the systemic conditions that affect the students don't their parents.
Why aren't there *more* private schools? Cost prohibition. You should know the answer to all of these questions fully if you're even remotely familiar with Sidwell Friends School (which I'd imagine 85-90% of the U.S. population is not (and a good chink of the name recognition comes fro Sasha and Malia's attendance there).