A teacher not able to fathom being corrected by a student. Terrible and terribly common. Afraid to lose their authority, perhaps? I had this happen to me at around 8 or 9yo : I corrected my teacher on a specific conjugation (the infinitive of a verb), but she wouldn't admit she was wrong. That day I swore I'd respect anybody in a discussion, even when I thought I was right and they were wrong. I would consider their take at the minimum