If it helps my DS says that with maths you have your lesson - but then it's up to you to do the homework and learn what was taught and be ready to move on to the next lesson and part of the syllabus.
The teacher does not have the time to explain
how it works. It's a very different style of independent learning.
You are expected to listen, learn get on with it
If you don't at his college keep up them they remove you from the course.
So as a parent if your DC can not keep up its not the fault of the teacher. They are there to show and explain what you need to learn in your own time.
Your DC has to suck it up, be full of grit and determination and just learn it and get on with it
My DS had twice as much maths as normal for obvious reasons and was doing hours and hours of homework because you have to write it all out properly step by step. Even if you know the answer straight away in your head. It didn't help that he'd leave it till the night before so would do 6-9 hours in one go.
I very much suggest to not do this if possible.
Get them to slow down. DS always rushes things so that's how he made his mistakes. He has learned the hard way to slow it down. In the A Level though there's not much time to reread your answers from what I remember him saying.