Primary school was the worst for me, because I was sent to a weird little school and several teachers seemed to be nuts, they criticised me relentlessly for being shy. Not disruptive, or naughty, or lazy, but too quiet in class. My parents kept all my school reports and I read them recently, it made me so sad to read how many overlooked the fact I worked hard, was good at sport and had lots of friends, they just really obviously disliked me just for being a quiet child. That school has since gone bankrupt, thank god.
Secondary - my head was too big. Being frigid, because I'd have rather cut my arm off than started doing stuff with the boys at my school. Having a weekend job.