Since this was in the horror section I expected it to be scary. No matter, it was still interesting. Supposing the narrator is a teenager, the language felt a bit too formal, especially when you throw in such modern things as a camera phone. I can't think of any young person who says "marrow." Huhm, actually, I can't think of any person—except for poets and old writers—who uses marrow. I did, however, find it clear, well-written, and to the point. It certainly kept my interest. Good job on the end there; I can't figure it out either, but I'm tempted to think she was imagining it all. Overall, I'd say good job. I enjoyed it but think you should loosen up a bit on the tone. Keep it up!

P.S. Your summary inspired me to write a short-short story about freaky science teachers; I'll have to thank you for that ^_^