LOL dumb kids. I knew a few kids throughout school that had learning disorders (typically high-strung kids) who would take anything anybody said extremely personal and freak out. That's probably what happened here - a kid got in trouble for standing on his chair, and convinced other kids that they needed to hurt the teacher. Lots of kids are easily led and most won't speak out about these things, just choosing to stay out of it rather than going to the teacher/school so they don't get in trouble with the other kids.
Seemed pretty elaborate to me...definitely a case of one kid leading the others though IMO.