There are some teachers who do not know how to teach math.
If a subject is difficult for your child, I’d probably take a non-credit class, or read up on the textbook, during the summer before having to take a credited class. This way, they have some knowledge of the course before they have to take it.
The way they teach math is stupid. I was helping my 8th grader with Pre-Algebra. Some of the questions were to work the problem “mentally” which means rounding and estimating. He would get answers like 12.75 and the answer would be 13. Teacher counted it wrong. They give them one day on the topic and they take a quiz on day 2. The next day they move on. Later they have a test covering 4-5 concepts then never touch it again. There is no mastery to the curriculum.