At my blue blood private school, I had a math teacher who explicitly told my dad that he gave me a bad letter of rec on an MIT summer camp application, because as a black person affirmative action would make life too easy for me.
I'm happy it was only a summer camp and not my real college admissions the following year.
Even though I was a top five math student in my class across the entire private school, he and the dean of the math department gave me lower grades for the same work. They also didn't let me test out of classes (wouldn't show me test results), etc.
Thank God for SAT II's and AP exams.
I destroyed those tests. 5's and 790's.
Highest marks in the class for Math SAT II's.
But it didn't help my GPA from those biased teachers.
I did get into MIT for real the next year.
Standardized tests helped protect me from teacher bias.
Ultimately, the world is just a mess.
Now, I just focus on teaching people that the only fix for our problems will not come from mankind (to see what I'm talking about, take a look at: https://jw.org).
Humans are a mess.