For a less extreme example, a large group of tech folks I was hanging out with compared notes on US high schools. My high school was ok (one random site ranked it 35%-ile among schools in WI, another one rated it well above median), which made it bottom of the barrel among tech folks. Most people went to high schools where basically everyone graduated, very few people were in the "reduced price lunch" income bracket, etc., which means they were in high-end high schools.
I don't think there's anything wrong with attending an elite private high school or being wealthy enough to live in a great school district, but the rate feels surreal to me. The thing that really surprised me when I looked at the data is how heavily top companies recruit from top schools and then how heavily top schools "recruit from" high income families.
The median student at a top school is > p90 parental income and even at a "merely good" school, the median student is > p80.