Ethnicity is not the only factor strongly correlated with scores. Parental education and income are significant also. The schools publish some data on that.

The tests themselves have problems. As one poster pointed out, the schools drill the kids for the tests. Additionally, it definitely happens, even (especially?) in the best schools, that a teacher will say to little Johnny “Did you really mean to fill in that bubble? Can you think again about it?”

Some kids genuinely get a perfect score on every test and subset. So the tests do not provide information at the high end.

Two of the schools mentioned, La Jolla Elementary and Hawthorne, have seminar classes. They take some of the smartest kids from other schools mentioned, like Torrey Pines and Curie, so averages are distorted.

But then it happens that teachers or schools don’t want to lose their best students, so they give kids the message that the test for seminar eligibility is not important.

At higher grade levels, pupils know that test scores are important to the teachers and schools, but not to their own futures. So some deliberately score badly to get back at teachers.