A child will receive multiple warnings during the year that work is not being handed in, that work handed in is not up to standard, that class participation needs to be increased. There will be weekly tests and many periodic exams too, including an exam at the end of each semester, the results of which will be tracked. The beauty of the GPA system is that you can't spend a full semester sitting in class and producing no homework andnnot participating in discussions, with teacher and parents surprised at the end of the year when you flunk your exams.
It is very odd to fail an entire year. Most high schools have many ways for students to improve their performance, from tutors to social workers for support if the student is experiencing issues that are interfering with performance. In a year long class, a student can change to a lower level at the start of the second semester if the first semester turned out to be too challenging, or can change to a one semester class in a different subject.
The level for a child with an IEP will be individual.
Nobody would ever know or care what grades anyone got in any given class.
There would not be a huge variety of expectations or attainment in any given class because tracking / streaming means students do classes geared toward their ability and learning style. At the end of your four years of high school, if you're on a typical honors style track, you'll find yourself seeing a lot of familiar faces in all of your classes. These will be students who hope to attend elite universities, and they will be doing mainly AP level courses.