Headteachers should deny teachers time out for health appointments and family events, even if their colleagues are happy to cover for them, an expert on new "rarely cover" legislation has warned school leaders.
Stephen Szemerenyi, pay and conditions consultant at the Association of School and College Leaders, said teachers' visits to the doctor or dentist should be in their "own time", because of the cost of finding alternative cover.
Hospital visits should be allowed because they were less flexible, he said.
Heads needed to decide exactly what other sorts of leave could be condoned, with or without pay, including events such as going to a child's graduation or nativity play. As a headteacher's final decision on what to allow or disallow could leave staff feeling "hard done by", they should be consulted, he said.
Addressing a seminar at ASCL's annual conference last week, he said that "voluntary arrangements" between teachers to cover for exceptional staff absence, training and school trips were "completely out", because of the legal implications.
"If the staff do it without your knowledge, it's a disciplinary matter," he said, "and if they do it with your knowledge, it's against the law."
He suspected there were "all sorts of illegalities" taking place in schools on the new rarely cover rules. "But at any point, you only need one person to complain and you've had it," he told heads. "Governing bodies could use this as a basis for dismissal."
Last week's ASCL conference was the first since the controversial introduction of rarely cover in September as the final piece in the jigsaw of the 2003 Workload Agreement. It is designed to ensure teachers make the best use of their non-contact time, rather than covering for absent colleagues.
But the rigidity of the rules has frustrated some headteachers.
Pete Kubicki, head of Cordeaux School in Louth, Lincolnshire, claimed his staff had been "under-whelmed" by the freedom the new laws gave them.
"They're saying it's too stringent, they want more flexibility. If you're going to have a professional culture in school, we need to have the flexibility to respond compassionately to things."
A number of heads at the conference said they thought that cutting back on allowing staff to go to exceptional events during school time would simply result in increased levels of sickness.
Sue Moore, headteacher of the Queen Elizabeth II High School in the Isle of Man, said teachers at her comprehensive were tending to take more trips in their own time, including school holidays.
The stern warnings from ASCL officers come after headteachers' leaders warned the children, schools and families select committee that rarely cover arrangements were reducing the number of school trips that schools take. The TES also recently reported that training centres had seen a dip in the number of bookings for CPD as heads try to avoid the costs of bringing in additional cover.
Committee chair Barry Sheerman launched an attack on teaching union leaders, telling them: "So you've negotiated something that's ended up with a deterioration of the educational opportunities of children up and down this country? You have a more comfortable life for your members, but damn the children's prospects?"
He told union leaders they seemed "complacent" about the unintended consequences of rarely cover. But Mary Bousted, general secretary of the Association of Teachers and Lecturers, said the problems could be resolved through "effective leadership and effective planning".
John Morgan, president of ASCL, said excursion weeks or days could be timetabled into the year, so that teachers would accompany pupils out and remove the need for cover, he explained.
DCSF to get tougher on the surreptitious savers
By Kerra Maddern
Headteachers who have squirrelled money away in an attempt to survive feared budget cuts will be penalised by the Government, ASCL officials have warned.
Those with excess balances will find the money "clawed back" as the Department for Children, Schools and Families takes a tougher line on over-healthy bank accounts, the organisation's funding experts have predicted.
They are now set to meet with DCSF bosses to argue that headteachers should be allowed to keep savings over 5 per cent - the current limit - because of tough financial years ahead. If they are not allowed to do this, school leaders will not be able to fund wages in 201011, ASCL policy director Malcolm Trobe told delegates at the conference.
"I predict that when drawing up budgets many headteachers will look to have slightly bigger balances than they would have chosen to have to cover staffing costs," Mr Trobe said. "We are taking a strong view that the DCSF needs to let that happen, and are meeting with them to tell them it may be an outcome."
A rise in National Insurance in April 2011, a possible pay rise for support staff, and demographic changes that make it harder to predict the numbers of pupils - and therefore staff - could lead to headteachers keeping the money as a safety net to ensure stability, Mr Trobe said.
The DCSF wants schools to make efficiency savings of 0.9 per cent over the same period.
"Around one in six schools have a budget deficit. When money is tight it's not a good place to start looking for cuts," Mr Trobe said.
The crossover between the financial and academic years will also prove problematic for headteachers, ASCL predicts. Headteachers could take on extra staff for the 201011 financial year, only to find they can't afford to keep them on a few months later when council education budgets are finalised.
"Those who over-commit for staffing for this September will find themselves with a real headache in the next financial year," said Mr Trobe.
Conservatives' back to basics plan 'will not equip' children for 21st century
By Kerra Maddern
Conservative plans for a back to basics, traditional curriculum will leave children unprepared for the modern world of employment, headteachers have warned.
Making children sit in rows, recite poetry and learn mental arithmetic would be a "backwards" step, school leaders told shadow schools secretary Michael Gove at the ASCL conference.
They also questioned Mr Gove's plans to raise entry standards for teacher training courses because they think it would deprive the profession of talent.
Mr Gove announced that the Conservatives want more private schools to switch to the state sector by becoming academies.
Meanwhile, Liberal Democrat leader Nick Clegg and his education spokesman David Laws used their slot at the conference to promise #163;2.5bn of extra investment - as long as teachers "raised their game".
Both the opposition parties said politicians must have a radically different relationship with teachers if problems in the education system are to be tackled.
Mr Gove has now given detailed plans of his curriculum reforms, which he says parents want. But former ASCL president Sue Kirham said she "couldn't bear" the thought of her grandson and other children having to follow the new "backward" lessons.
Other members clapped as she said: "Do you really believe our current 14-year-olds are going to be motivated by this sort of curriculum and it will prepare them for their future lives? I was taught like this in the early 1960s and it didn't equip me for life in the 20th and 21st century."
Mr Gove said the changes were needed to help "celebrate knowledge". "It's what parents with children in private schools want," he said.
Mr Clegg said a Lib Dem government would "relinquish" control over schools and stop "legislative hyperactivity".
"We will give you money, but we will expect you to raise your game. This will be a new relationship between government and schools built on trust rather than blame."