While $56,000 per year might sound like a lot to many people for K-12 tuition, this is really a drop in the bucket for many of the folks who live in San Francisco.
I think what is left unsaid, though, is that the school environment is very helpful to select for other folks of the same class. These schools hire many of the same teachers and have a lot of the same methodologies and standards as public schools, so it is no secret that the school itself does not necessarily provide academic rigor; it is a lot of after-school prep and outside resources anyways.
Nothing beats the connections you can make tho
Tuition costs at private schools in San Francisco according to the SF Chronicle
Average private high school in the city is $56k per year. Middle school $30k and elementary $28k
The Catholic schools on this list stand out as having substantially lower tuition and many are regarded as being some of the top schools in the city