I live in the US. My daughter switched classes last year. We transferred to the school system before the start of the school year (a much better one than the previous one which mostly catered to children from lower class families) and as a result, she was behind her classmates for her grade and age group.

The teacher was openly derogatory towards her when she didn't understand a concept and refused to help her during open study periods. The child was flat out depressed when having to do anything with the class. We had enough and had a conference call with the principal, her assistant, and the teacher. Our kid was in a new class the next day.