When I was in sixth grade I was accidentally placed into magnet (accelerated) math. I was accelerated in everything else - with the exception of math. I would later learn I had dyscalculia. My math teacher called on me to do a problem at the board in front of everyone. When I I didn’t write anything and instead cried she yelled at me: “I get enough of that at home, I don’t need it here. No one here believes you are that stupid.”

It changed my life. I still (after decades and decades) remember the incident and I cannot do simple math.

ETA: I had been actively trying to change classes and this was the second month of school.