Heads are breaking the law by forcing teachers to cover for the classes of absent colleagues, a survey has found.
School leaders are flouting new regulations which say their staff should only step in "rarely" when others are away, according to a poll of 1,000 teachers by union the NASUWT.
Union bosses have called for non-compliant schools to "face the full force" of punishment.
More than 60 per cent of teachers surveyed said their school was not complying with the rules, which came into force last September, and 25 per cent are still asked to cover three to four times a term, the study found. A third said the absences they were asked to cover were "foreseeable", rather than emergencies.
Heads who took part in the survey said their worklife balance, access to training and chances to take children on educational visits outside the classroom had all worsened since "rarely cover" was introduced.
Chris Keates, general secretary of the NASUWT, said she was concerned by the "negative effects of the worryingly high level of non-compliance by schools".
"Some schools are operating without statutory provisions and guidance and even misapplying the regulations to introduce or justify deleterious changes to teachers' working conditions," she said.
"These schools are ones which often regard the contractual changes as perks for teachers rather than improvements to working conditions to enable teachers to raise standards.
"It is this negative attitude which is behind some of the punitive strategies schools have threatened such as cancelling education visits, preventing teachers accessing professional development opportunities and preventing teachers attending important family occasions such as their child's graduation.
"There is absolutely no need to cancel any of these activities."
Ms Keates was partly responsible for the introduction of rarely cover through her union's membership of the Government's social partnership. She said the problem with the policy was only that it was being ignored by heads.
"This change was agreed in 2003. Schools have had seven years to implement it. Those that haven't must now face the full force of the compliance legislation," she said. "Non-compliance compromises teacher effectiveness and educational standards. Schools which fail to abide by the law are disadvantaging pupils."
Around 56 per cent of those surveyed said they were not able to take children on school trips, 19 per cent had been refused permission for hospital visits, 21 per cent were not able to get compassionate leave and 27 per cent were not allowed out for routine hospital appointments.
The report accompanying the poll results says only a small number of teachers have benefited from rarely cover. Schools have to comply with the rules, which are set out in the Apprenticeships, Skills, Children and Learning Act 2009.
CREATIVITY, PLANNING AND COVER SUPERVISORS
After 32 years as an English teacher, Paula Roe is now benefiting from the "rarely cover" rules that free her up from standing in for colleagues.
The system has been successfully introduced at Redhill School in Stourbridge, West Midlands, Ms Roe said, but not in all schools across her local authority. "I know colleagues elsewhere who have covered as many as ten or 12 periods since September," she said. "That means not all heads are complying with the rules."
She said heads needed to be "creative" and plan properly, and her school benefited from employing three full-time cover supervisors.