I LOVE bio :) Had a really great teacher but she went off to have a baby . . . now we have the biggest joke of a teacher who is not actually a biology teacher he is a physics teacher. And btw, bio people may leave the lab smelling bad but then some of us turn into chem people and make it smell...
Love the kinda post-modern thing ur thinking about for the ending. Imho i think it could be cool if u had the kids jumping on the spikes but then a flashback to deal with why the spikes are in the water; i reckon that's the really interesting bit.
I've got 6243 words . . . started revising. Mind you, I only started writing about two weeks ago and did it all over four days--exhausting but the only way it works for me :)