I don’t believe the UC’s consider the high school’s API scores in evaluating a student. UC’s look at the child’s GPA, SAT scores, rigor of the high school curriculum taken, EC’s, etc. A high school student can still attain a high GPA, high SAT scores and a rigorous curriculum, even at a lower API school like Mission or Balboa High in SF. These high schools do offer AP calculus, Spanish, Chemistry, etc. There, the competition is probably not as keen as at Lowell High.
I don’t know how these kids performed at Cal, but many students change majors all the time, even ones from Mission or low API ranking schools.
A couple of my friends’ kids, though accepted to Lowell, chose not to attend and instead attended the private school, University High, where they felt the competition for grades was not as intense as at Lowell.
Subsequently, these kids were also accepted to UCB and instead chose private schools like Georgetown, Claremont College, etc. One who went to Georgetown later went on to an Ivy League dental school.