Ensuring teachers get enough time to plan lessons is a priority, the new chief of the National Association of Head Teachers says.
Mick Brookes was elected in April
New rules mean teaching staff will be spending 10% of their time on planning and preparation of pupils' work.
Incoming general secretary Mick Brookes said he would ensure budgets were large enough to implement the regulations.
Mr Brookes takes over from David Hart, who stepped down after 27 years at the helm of the head teachers' union.
Issue a 'headache'
The new government regulations coming into effect mean that teachers must spend 10% of the working week on planning, preparation and assessment (PPA) - and there are worries this could leave shortfalls in staffing.
Other staff will have to look after the class during that time and has raised fears over the role of teaching assistants, where they are available to supervise pupils.
The 57-year-old former head said the change was among a raft which would make autumn "interesting" for the profession, not just the union's 38,000 members.
"That's going to be a headache, not just for our members. A lot of schools have clobbered together something for this term, but sustaining that will be the issue," he said.
"We need to make sure there's maximum pressure so budgets will sustain the arrangements put in place."
Otherwise, he said, resources such as special needs provision could be threatened.
"We'll be turning the clock back in a lot of the gains this government has made."
The government has said PPA will raise standards in schools and fewer than 15 schools in England have said they will have difficulty implementing it.
Mr Brookes said NAHT members were concerned about how they would manage PPA on top of other high-profile issues this term.
They included Ofsted inspection reforms, extending school hours, maintaining healthy schools and inclusion of special needs pupils.
Head at Sherwood Junior School, Notts, for 20 years
Former NAHT president
Plays bass guitar
Rides a motorbike
He also pledged to put pressure on the government to re-visit the Tomlinson proposals for an overall diploma to embrace existing qualifications for 14 to 19-year-olds.
Pupils were being "turned off" by the secondary curriculum, he said, which needed to become more "accessible, broad and balanced".
David Hart is retiring to spend more time with his wife and their horses at home
Mr Brookes paid tribute to Mr Hart's 27-year-tenure and admitted the general secretary job will be a big shift from life as the head teacher of Sherwood Junior School. But he would not be drawn on which will be the longer working week.
"It's going to be a big change, it already is," he said.
"I've done a lot of work since the election to get to know our staff and members and the issues they're most concerned about.
"It's my job to take that on board and see what we can do about it."