First findings of a survey of members of NASUWT reveal widespread bullying with allegations that school managers are clearly overstepping the boundary of hands-on management.
One in five victims said they had left their job rather than be subjected to bullying and another one in 10 said they had surrendered posts of responsibility. Other teachers reported loss of confidence, dread of going to work, and sleepless nights.
The survey identifies the bully as predominantly male, aged between 41 and 50 and most likely to be in a senior position in an independent or grant-maintained school.
But delegates to the union's annual conference in Eastbourne last week also railed against governors for daily, unannounced entry into classrooms, accusations of insubordination, and threats to future employment. They also complained about parents who assault staff and threaten to take their children away from school if their wishes are not granted.
The survey of 3,500 members revealed the most common forms of bullying as destructive innuendo and sarcasm, intimidatory use of discipline and teachers being shouted at in front of colleagues and set impossible deadlines.
Officials claimed a male head had grabbed a pregnant teacher and dragged her into his office before berating her for getting pregnant six months after gaining promotion, and said a female head "went round clobbering people".
Les Roberts, an assistant secretary, said: "What we have found is a kind of institutionalised bullying. Bullying designed to frighten and humiliate. Some teachers are dying and others are driven into permanent illness or disability.
"Schools are under pressure from outside and some management teams are not coping and are transmitting that pressure on to staff. We call it cascade bullying."
Violence to property or the person was very rare and although bullying took place in all kinds of schools, the greatest risk was in those regarded as "dictatorial or authoritarian" in style.
A female primary school teacher said: "The deputy head is a bully. He used to corner me (and others) and put his face very close to ours, look us straight in the eye and grill us. Sometimes he'd shout in public, but often he'd pick a moment with no-one around - that was worse. He would cause a public scene over the most stupid, trivial things. He's acting head at the moment and we do things because we're scared of the consequences."
A male teacher in a local authority secondary reported widespread bullying by his head and deputy and related: "What was an excellent job with hard working staff is ruined (following arrival of new head) and cannot be put right. Help set me free. Ninety five per cent of staff feel the same. I can't wait to retire - if I make it!"
A teacher in an independent school told of the dread felt at the end of each term while awaiting a summons to the office to be berated for being hopeless.
A male secondary teacher bullied by a female head of department said: "She overloaded me with unnecessary extra work, made unreasonable demands, needlessly questioned everything I did, undermined my authority with pupils, discredited me in the eyes of parents, pupils and colleagues, displayed a contemptuous, insulting and unco-operative attitude towards me, generally made life as difficult and uncomfortable for me as possible, and obstructed me in the carrying out of my duties.
"I am the fifth person to be made ill through stress in two years at this school. Now I am chronically ill and my chances of a full recovery are practically nil."
The NASUWT last week agreed to campaign for laws to combat bullying in the workplace and to enlist the support of the TUC in its fight.
Speakers told the conference of a head who insisted on a dress code which limited the number of months women teachers could wear trousers, and teachers told to re-arrange furniture only to be ordered to move it back a few days later.