The outspoken head of Ofsted has hit out at teachers who complain their jobs are "too stressful" and make excuses for poor performance.
Sir Michael Wilshaw suggested head teachers needed reminding what stress really was.
Speaking at an education conference, he said heads were better paid and had more power than ever before.
But the ATL teaching union said official figures demonstrated how stressful teaching can be.
Sir Michael told a conference of independent school heads in East Sussex that in the past, poor teaching and poor performance had gone unchallenged.
He went on: "We need to learn from this and challenge those who have power invested in them to make the difference, but too often make excuses for poor performance - it's just too hard, the children are too difficult, the families are too unsupportive, this job is far too stressful.
"Let me tell you what stress is. Stress is what my father felt, who struggled to find a job in the 1950s and 1960s and who often had to work long hours in three different jobs and at weekends to support a growing family.
"Stress is, I'm sure, what many of the million-and-a-half unemployed young people today feel - unable to get a job because they've had a poor experience of school and lack the necessary skills and qualifications to find employment.
"Stress is what I was under when I started as a head in 1985, in the context of widespread industrial action - teachers walking out of class at a moment's notice; doing lunch duty on my own every day for three years because of colleagues who worked to rule; covering five classes in the sports hall when there was no-one to teach them.
"Stress was, in the days before local management of schools, writing letters in triplicate to the local authority asking for a brick wall to be built in the playground or for a bit of extra money to keep an excellent maths teacher - and not receiving a reply for weeks."
Sir Michael said that times had changed and that heads were now in charge, with better pay and more independence, power and resources than before.
"We need heads who know what a privileged position they are in now and who can use their new-found independence well - people who roll up their sleeves and get on with improving their schools, even in the most difficult circumstances.
"What we don't need are leaders in our schools whose first recourse is to blame someone else - whether it's Ofsted, the local education authority, the government or a whole host of other people."
Dr Mary Bousted, general secretary of the Association of Teachers and Lecturers, said Ofsted should concentrate on helping schools improve and stop criticising teachers and heads.
"It is really not helpful for Michael Wilshaw to rubbish the amount of stress teachers are under.
"The pressures on teaching staff and heads are enormous and growing due to the constant churn of government initiatives, tinkering with the curriculum, introducing new tests, and pressure to get pupils through exams to prove their school is performing well.
"And Ofsted is part of the problem with its continual changing of the inspections goal posts, and ridiculous demands for lessons to be exciting at all times.
"Teaching is the occupation with the third highest amount of work-related stress according to Health and Safety Executive figures."