Mick Brookes likes to ask visitors to his school to play "spot the teaching assistant". "It's part of my risk assessment," he says. "At the end of their visit I say, 'OK, which one was the TA?' Nobody's got it right yet."
His school, Sherwood junior, in Nottinghamshire, is well ahead of the game on workforce remodelling. Assistants help to plan lessons and even take whole classes within a controlled framework set by the teacher.
Mr Brookes says this has lifted a big weight off the shoulders of his teachers, giving them what the Government says all teachers must have from September -planning, preparation and assessment (PPA) time, which represents 10 per cent of their scheduled teaching time.
But while the school can offer its teaching staff a happy working environment, the changes have come at a cost.
Mick Brookes brought in extra PPA time ahead of the deadline in the mistaken belief that the Government would give schools extra funding to do it.
In July, he will leave Sherwood after 20 years and regrets that, despite leaving his successor a good school, part of his legacy will be a hole in its budget. He estimates that within two years it will leave the school Pounds 30,000 out of pocket.
From September, he will move on to a much bigger fight when he succeeds David Hart as general secretary of the National Association of Head Teachers.
Mr Brookes was recently swept into office by NAHT members who have lost patience with the Government, worried that they cannot afford to implement the final phase of the national workforce agreement.
He gained more than twice as many votes as the NAHT executive's favoured candidate David Hawker, director of children, families and schools at Brighton and Hove council.
He says the Government could solve the dispute by giving primaries parity of funding with secondaries. At present, they lag 30 per cent behind. "If you translate that to our school, where each pupil brings pound;2,000, then between Years 6 and 7 each pupil is worth pound;600 more," he says.
He adds that while workforce reform has worked at Sherwood (though he stresses this is not a model that would work in every primary), his school highlights the need for extra funding.
"There's a willingness to make it work," he says. "I have not yet met a colleague who does not want to make this work - it is a historic agreement that primaries for the first time enjoy some of the time away from the children that their secondary colleagues have enjoyed for time immemorial.
"Second, this is about the capacity in your school. This hinges on having teaching assistants who are willing and able to take on this additional role, and the risk assessment of that needs to lie with the head. But it also requires the additional funding to enable that to happen."
Sherwood junior is in an imposing red-brick building in Warsop, near Mansfield. Mr Brookes joined as head 20 years ago, after the miners'
Today, with the closure of collieries the area has high unemployment and problems linked to social disadvantage. Almost a fifth of its 253 pupils claim free school meals, though the proportion eligible is higher.
In an inspection two years ago, the Office for Standards in Education declared it a good school. Its key stage 2 Sats results have seen a steady improvement in recent years. Last year, 80 per cent of pupils gained level 4 or above in English, 75 per cent in maths and 98 per cent in science.
The school started to give its teachers PPA time a few years ago when rolls were rising. Mr Brookes found he could afford a member of staff to take sport one afternoon a week for each class, allowing teachers 5 per cent non-contact time.
The other 5 per cent has come thanks to the school's teaching assistants.
TAs are treated well - Nottinghamshire pays just below the starting salary for a newly qualified teacher. Mr Brookes has also encouraged them to gain qualifications and says they are respected by teachers and pupils.
Each year-group has two teachers and one TA. One afternoon a week, the assistant takes over after the teacher has introduced the lesson.
Sometimes, the TAs will take whole lessons, but only after they have sat down with the teacher to plan it.
"They are quite capable at picking up what needs to be said, and very confident," says the head. "They have been confident in speaking to smaller groups, and they seem to have taken it in their stride adapting that to a large class."
After a successful experiment last June, this year the school altered its TA contracts, allowing them to be paid at a higher rate when they were in front of a class.
Mr Brookes says that now, with rolls falling, the school has had to subsidise PPA time with pound;10,000 from its reserves.
"Some tough decisions will have to be made in the future," he says. "Are we going to have to dismantle some of the PPA time, or are we going to start undoing some of the structure and support we have in school - for instance, taking TAs away from children with special educational needs? Or are we going to be looking at losing a teacher?"
But the benefits are great. Writing has improved because teachers have had the time to focus on pupils who need help, he says. And the staff feel valued.
"If they feel they're being well looked after and their needs are being met, then there is a loyalty and a willingness to go that extra mile" he says.
The school has also changed the status of its TAs.
He says: "We have some challenging children who have been known to say in the past, 'You can't tell me - you're not my teacher.' I don't hear that any more. They see the TA having equal respect to the teacher. And that has given us a really strong staff team."
Year 6 teacher and ICT co-ordinator Bill Dennis says the PPA time has given him and his colleagues vital breathing space.
"It has made a huge difference knowing that every week you have half a day to have a breather and catch up," he says.
"It gives you the chance to do some really in-depth marking, or to prepare things for your next lesson.
"And the time you get allows you to think, 'How can I make this a little bit more interesting tomorrow?'"