I was the only person my cousin could turn to for help when he was taking math in high school. When he asked me for help, my first instinct was to help him find the relevant information in his textbook. But the textbook wasn't helpful at all. First, he was often working with things that weren't indexed; even though his homework was from the textbook's supplemental materials. Then, the text was hard to understand. It just wasn't written very well. Finally, the whole thing was just too busy, with many different fonts, all sorts of margin notes, many footnotes, and colored boxes surrounding text. This made finding information harder and just gave me a headache.
I had the same experience. My little sister just finished HS a year or two ago, and I helped her with her homework quite a few times.
The books were useless. It was nearly impossible to find concepts in it, and when you did the description was often relatively short, relying on an example that was often poorly constructed.
In the end, if the book didn't jog my memory I would have to Google the concept to find a better page. The book might as well have been nothing but problem sets.
I never met any of her teachers. I got the impression that at least one of them wasn't qualified to teach math, but that was 2nd hand information through the lens of my sister, so I can't be sure how accurate it was.
