I have to agree with this. For high school students you may be expecting a lot if you want them to read through six or seven full length novels, and even if they do manage to read through all of those novels, you probably will just barely scratch the surface of good science and fantasy fiction. I would pick one to three medium length novels, and cover a much broader selection of short stories. A lot of the more well known authors have written short stories at one time or another, or have short stories that accompany their major works.

For instance, George R. R. Martin's Game of Thrones is a very interesting novel, but might be much too long for high school students to reasonable read without taking up a good third of the year. His Hedge Knight novella on the other hand is much, much shorter, and might be the kind of thing you could cover in a week. That might even be too long. Short stories that are twenty to forty pages in length, and can be covered in a couple of days before moving on might be the best way to introduce the students to the wide range of science and fantasy fiction that exists.