@Mor - That's the theory, but unfortunately I think the reality is often that high school students are learning how to read properly as well. Or at least how to write.
I don't think many teacher training courses do enough emphasis on making sure the whole class is being helped. So many teachers will just focus on the middle of the road kids, or on the lower kids, or on the higher level kids and will leave everyone else to struggle as best they can.
Designing a course at any level that can suit everyone in the class takes a lot of ability.