Teachers are being swamped by the huge amount of marking now required to comply with Ofsted inspections, headteachers have warned.
Inspectors have stopped grading individual lessons but have increased their scrutiny of assessment and marking, adding considerably to a workload that is already at risk of overwhelming the profession.
Russell Hobby, general secretary of the NAHT headteachers' union, is lobbying Ofsted to drop its emphasis on pupils' books, arguing that "marking is the number one problem of teacher workload". He is due to meet with Ofsted officials next month to press his case for reform.
This week, education secretary Nicky Morgan conceded that the inspection system was adding to concern about workload.
"There's no doubt when I go around the country talking to teachers - Ofsted and the accountability regime is one of the things that really does contribute to workload," she said. "I think in any regime like Ofsted there are always going to be tweaks that need to be made, partly because of new areas coming on line."
The decision by Ofsted to drop individual lesson grades - heavily criticised for being unreliable - was warmly welcomed by teachers. But inspectors' focus on marking when judging the quality of teaching has failed to win support.
Kevin Bullock, headteacher of Fordham CofE Primary School in Cambridgeshire, said the level of scrutiny was pushing teachers to go part-time. "Teachers I speak to in a variety of schools want a four-day week and it's all to do with paperwork," he said. "They work four days because they can catch up on the fifth day. It sounds bonkers but they fear that if they do five days they will end up working for seven.
"It's down to this forensic study that Ofsted do. It has gone absolutely crazy. Ofsted come and look at books and you have to justify every child's progress, you have to have evidence in books."
Alex Quigley, an English teacher and director of learning and research at Huntington School in York, said the pressure on teachers to prove pupils' progress through detailed marking and comments in books could backfire.
"Quality and quantity are not one and the same," he said. "Good-quality feedback for learning is a great, high-impact strategy. There's no shortage of evidence that proves feedback works when it is judiciously done.
"But there is a difference between that and a treadmill of endless assessment that is just to exemplify progress for Ofsted. Ironically, the more feedback you give, the less attention the students pay to it.
"Some work in class can mean there is nothing for me to assess: there may have been a discussion and students made notes. So you end up with teachers having to contort what they teach to get an assessment out of it."
A new framework for school inspection was introduced in September. Inspectors continue to observe lessons, but they now judge the quality of teaching on other factors including the setting of regular homework and the quality of marking, assessment and feedback.
Last month, Ofsted published a "clarification for schools" document that said inspectors did not "expect to see unnecessary or extensive written dialogue between teachers and pupils in exercise books and folders" (bit.lyOfstedClarification). But Mr Hobby pointed out that this failed to make clear what inspectors did expect to see.
"Marking is a really important part of assessment and teachers ought to be doing it to help children's development," he said. "But heads say the emphasis on workbooks means they have to make sure that it looks like frequent assessment is taking place or they will face negative interventions [from Ofsted].
"If we were confident and knew what inspectors were looking for then we wouldn't need to overcompensate."
The government recently launched the Workload Challenge to gather evidence on excessive working hours, prompting more than 30,000 responses from teachers (have your say by 21 November at www.tesconnect.comdfe).
A survey by the NUT in September also uncovered workload concerns. Marking was highlighted as the single biggest problem: 80 per cent of respondents said that assessment expectations were excessive.
An Ofsted spokesperson said: "Ofsted published a myth-busting document in October following extensive and productive consultation with all teacher and headteacher unions. The document has been well received.
"It makes it clear that Ofsted does not expect to see unnecessary or extensive written dialogue between teachers and pupils in exercise books and folders. It is up to schools, not Ofsted, to set their policies and expectations for marking."
`Marking books can be endless'
Richard Farrow, who teaches a class of 32 Year 5 children at St Mark's CofE Primary School in Stockport, says teachers feel under pressure to start a dialogue with pupils when marking.
"You mark a piece of work, then you leave a question for the child. Then they write a response and you can comment or respond on that," he says. "The problem is it leads to a lot of re-marking. You have to keep on going back through the books to the day before and the day before that - it can be endless.
"You have maths and English every day and, say, history in the afternoon. You have 32 x 3 books to mark. You can do the topic marking at the weekend, but every day you have English and maths.
"It means pupils have less time for things like after-school clubs. It was a big victory when they [Ofsted] removed lesson grading but the kickback is that marking has increased."
Read more from teacher Alex Quigley on interpreting Ofsted's feedback requirements.
Primary school teacher Jo Brighouse discusses the increasing pressure of marking.