i recall reading The Lottery in school, Poe at a few points, and prior to those a dark story called Peppermints in the Parlor.
so i dont think school is devoid of horror persay. i think the gunslinger series is a little young of a novel for you to be able to get it in tho.
then again i dropped out at a young age, i couldnt say what kind of english curriculum was available past 9th grade
now im in college, and currently taking eng 102. we have an entire two weeks worth of work devoted just to Poe.
we recently read The Yellow Wallpaper by Charlotte Perkins Gilman, i highly recommend it!
it is a shame about King tho... im curious as to why he isnt in any of the english books. perhaps its notariety that will come to him after his death... but i definately think he is one of the most modern writers that is deserving of being taught in the classroom, for sure!
try to get some short stories from Nightmares and Dreamscapes into the classroom! Chattery Teeth, for example is something good for younger kids by King