A few thoughts on this.

1. Firstly and most obviously, this is a vivid, brilliantly written piece, utterly absorbing, full of thoughtful, self-aware reflection, and deserves to be read by everyone on Medium.

2. Reading this, I recalled two incidents from my own childhood where I was a participant in bullying (around the ages of about 8 or 9). I am pleased to say my father took a very dim view of both incidents, and I was severely punished, quite rightly. To this day, I have a deep, deep hatred of bullies and bullying, but part of the reason for that hatred is the cringing shame I still feel having participated in both incidents. Like you, it was quite out of character, I had no excuse, and knew I shouldn't have done it, but the bad angels prevailed for reasons I still can't explain. And I know exactly what you mean about it happening as though you were outside yourself.

3. As a father myself, I told my own children, both of whom were far more well behaved than I was as a child (they're now 14 and 19), that they would never be in trouble if they had to defend themselves in a fight, but that if they bullied people or started fights, they would be in trouble. Neither of them bullied anyone (to my knowledge) or ever started fights, but they have both had to finish them, as both have been targeted by bullies and attacked.

On the occasion my eldest was attacked in this way (he was about ten), he was worried he'd get into trouble as the school had reprimanded him (because he'd decided to solve his own problems rather than tell a teacher). But instead, I bought him a new toy for following my instructions to the letter. I don't wish to make any claim to being a great father, but as far as this is concerned, ultimately, the lessons of my own childhood were put to good use here.

Anyway, great piece, Sarah. :)