I was a sensitive kid getting bullied at one point and had a horrid 2nd grade teacher. Reflecting on her behavior as an adult, it was apparent that I was just a problem for her in her last year before retirement (there was a "Miss So-and-so is retiring" party we had to have as a class for her at the end of the year).
The bullying was bad enough that she would just remove me from the class and have me work alone in the library because I'm certain that it was easier than the alternative. This happened probably 30+ times until one day I broke down and started to cry because it was just a rough day, and I just felt very alone.
Librarians noticed, teacher notified, yelled at by the teacher privately for "being a disturbance", I then told my parents, Dad got insanely angry at the situation (rightfully so), and we met with the principal. I remember sitting outside of the office listening to my father destroy the guy verbally. I cried then too.
After the fact I didn't have to go to the library alone anymore, but she literally wouldn't respond verbally to me at times. I remember not being called on when I had the answer, being the only kid with a hand up. She just ignored me unless she absolutely HAD to respond (IMO abusive behavior towards a child). My grades went down and I was pulled from the gifted programs never to get back in. All of this happened within one school year.
I am horrified of what a teacher like that would have done to me with this tool.