Asians may be over-represented relative to their proportion in the population at large, but the question you should be asking is "are Asian applicants over- or under-represented among applicants with certain grades and test scores?"

This is a widely studied and easily Google-able topic. Private schools discriminate against Asian Americans is through the combination of Affirmative Action (favors non-Asian students), athletics (favors non-Asian students - completely bizarre to non-Americans) and legacy admissions (favors non-Asian students).

I attended a famous public high school where Asian girls (officially) had to meet a much higher grades+scores standard than others. Many lawsuits, so I'm not sure whether this is still in place.