^It's just that Ender's Game is an exceptionally problematic book (mostly because it's a pretty shitty book), and so would take an exceptionally good teacher.
Finally someone agrees with me! Got pretty much forced by a friend in high school to read it and it just left feeling kinda...meh. The twist is sort of clever but...that's about what I can say about it. It left me kinda untouched.
My personal suggestion for mandatory sci-fi is Contact. Both the novel and the film.