I had a funny experience a couple of years back.
The daughter brought home a maths' book and asked me if I could help her with a particular problem. There was an example at the top of the page. The example was using an incorrect formula for establishing the volume of a sphere. It was just wrong. A student looking at the example, would not be able to answer the questions on the page below it.
Before giving her the text book back, I circled the incorrect part with a red pen, and put a small 'x' next to it. Also put the correct formula with a tick. all very neat.
I told the daughter to point out the book's error to her teacher.
When she arrived home. I asked her if she had pointed out the error. She said she did. 'And what did the teacher say?' Teacher said; 'Don't put marks on text books.'