I think it is sad that people are assuming the boy was as fault. I say that as a teacher who has been assaulted, threatened with anal rape and thrown against a wall resulting in me loosing my baby. But those pupils do not represent most pupils, they are a small minority.
As a teacher who has taught in very tough conditions the choice is there to walk out, to reflect on what went wrong that day and change school or career.
I do feel for the teacher, while still thinking he is wrong, he clearly must have been under huge mental stress and teaching is an awful job when you are not mentally strong and start on that downward spiral. From what little I have read he has been a good teacher in the past and he as now lost that.