Senior staff are now watching lessons so often that some teachers are refusing to let trainees observe their classroom practice.
Teaching unions have called for a halt to the observation overload after thousands of complaints from their members. They say excessive scrutiny is damaging teachers' morale and confidence.
The National Union of Teachers said it would intervene if headteachers refused to limit scrutiny.
Chris Keates, general secretary of the National Association of Schoolmasters Union of Women Teachers, said: "In some schools observation is a euphemism for destructive, punitive and excessive monitoring, often carried out by those least in touch with the realities of the classroom."
One primary teacher in the south of England was observed every day for a term, she said.
There has been a sharp rise in lesson observations in the past 10 years because of increased school accountablity, performance pay and a new induction process.
Heads are now carrying out yet more observations to prepare for the new short-notice inspections that rely more on schools' self-assessment and which the Office for Standards in Education hopes will reduce the burden on schools.
Teachers' monitoring of each other is adding to the pressure. Bob Archer, a language teacher from Redbridge, London, said: "Schools have to be increasingly accountable to the latest learning styles and government initiatives. We now have an oppressive regime of departmental review: a mini-Ofsted - it is very stressful and very disruptive," he said.
Ms Keates fears that classroom observation could become even more punitive under plans to link it to teachers' pay.
The NUT has said observation for performance management should be limited to one hour per teacher, per year.
John Bangs, the NUT's head of education, said: "Erratic bunching of observations is highly confusing - they are rapidly becoming the bane of teachers' lives."
Both unions concede that lesson observation is a vital tool for professional development but warn that the scale of monitoring is creating intolerable pressure.
Education Secretary Ruth Kelly has asked the School Teachers' Review Body to look at how the monitoring teachers carry out influences progress up pay scales.
Sarah Murdoch from Canterbury, a PGCEstudent, said: "We are being told that staff have so many people observing them and criticising them... that the last thing they need is a student watching them and taking notes."
The National Association of Head Teachers has said observation should not be excessive, but David Hart, NAHT general secretary, added: "Some teachers need extra attention because their performance is not up to scratch."