See: https://www.latimes.com/california/story/2021-04-12/covid-co... Excerpts: UC admissions directors stressed that they evaluated students in the context of their own schools and communities to assess how much they challenged themselves and took advantage of available opportunities. A student who took all six AP classes offered at her school might be more impressive than the one who took six at a school that offere…
That is, they are biased towards top performers, not just high performers, even if one student's "merely high" is formally higher than the ceiling the other student hit. (The "winning" strategy then is to move to an underserved high school after an elite middle school, and hit the ceiling.)
Despite the "what are secondary effects?" school admins trying to "fix inequality" by creating school lotteries, ending gifted programs and focusing on "equality of outcomes not equality of opportunity", the only thing that has actually improved troubled schools is that smart kids with involved parents now actively seek out lower rated schools like Mission High so they can more easily rise to the top of the class and get a free ride to Berkeley or another UC.
There was an article about this exact phenomenon in SFGate a year or two ago so it is definitely a real trend.