I have not read through the story (yet), but I have to complain about the wording. It was a bit hard to follow the story at first. It didn't really explain who anyone was, or where they were for that matter. What age group are these characters in? They go to school, I got that, but what kind of school?
Don't make your readers guess at what you mean; explain the situation, make things clear. However, keep the story brief, don't drag on about tiny, mundane details. You want to explain the age group the characters are in, but if you don't want to specify certain ages, you can explain their grade in school.
Work on giving your characters some interesting quirks, too. Small variations to the base character design can make the character a lot more interesting. You can have a key character love lettuce so much he carries a head of it everywhere he goes. Then, when we see a head of lettuce with blood on it, we immediately become concerned for that character's safety.
...Okay, I read it!
The biggest problem I noticed was every single character seemed to have a name. Don't have characters say names so often, it's just too much. Nurse Betty didn't even need a name. You could refer to her as "the nurse" if needed.
