You know, I've actually been the victim of a teacher who loathed me and gave me different grades than the rest of the class even if I got the same number of answers right on the tests.
She enjoyed it when I would answer wrong, because she would let the entire class know that "Sibyl didn't get all the answers right, even though she is 'gifted' and supposed to be smarter than all the rest of you!" She enjoyed trotting out this humiliation on a regular basis. She occasionally made my grades lower because "You are 'gifted' and should therefore be held to a higher standard".
My mother went down there and had some angry words with her a couple times, and one day after a particularly bad bit of abuse from this teacher I went crying to the school counselor for help. The nasty old woman cooled down a bit, but she was always rotten to me. The other teachers were appalled by her behavior, but it's pretty hard to get a teacher fired, especially one with so much seniority, so she kept teaching. And abusing.
I think it's one thing if Moo didn't bother to call the school to get Bratley's lessons that he missed. When I was too sick to go to school, that was the procedure. The teacher would write up an assignment sheet and my mother would pick it up and I'd have to do the homework and take any missed tests when I returned. Moo is complaining about a lot of nothing, a nothing she could have prevented had she proactively called the school.
It's another if the teacher is actually being inconsistent and abusive of just a few students, as happened to me and a few other "gifted" kids.
I got my revenge, though. One of my other teachers and I were pals. She told me that Abusive Teacher had a terrible allergy to gardenias, and couldn't even be in the same room with them. I'd bring in cut gardenia flowers and hide them in Abusive Teacher's classroom. Whenever she was rotten to me, it virtually guaranteed she'd be sneezing and having runny eyes for a few days.