Trying to remember the name of a writer?

I've been trying to remember the name of a Horror writer. I read a book by him quite a few years ago but cannot remember his name.

Fron what I remember then book was set in a southern American town and centred around a group of school children. The school had an evil presence and strange things started to happen to each of the children and some of them started to be killed as the plot went on, and in the end only a few of the children were left to combat the evil inside the school.

One part I think I remember involved a fat kid on a farm and he was alone when he was attacked in a wheat field near a barn. I think his death involved a combine harvester.

Anyone got any ideas who the writer is and what the book was called? I think the book I read was the second book in a trilogy and I remember really enjoying the book and wanting to read the others by the same author at the time.