Anonymous letters to The TES usually get short shrift - especially if they are about headteachers. But one that arrived recently was different. It was word-processed, of course, but it was on school-headed paper. It was signed “a very happy teacher”. And it told an intriguing story.

Last July, this staffroom mole reported, a much-respected headteacher left after 18 “hugely successful” years to become a regional co-ordinator with Cambridge Education Associates - the company responsible for overseeing the Government’s new threshold and performance management schemes.

He was, as the writer acknowledged, one among many: there are a lot of heads leaving the profession. But this one came back. On the first advertisement for his replacement, back in the 2000 summer term, the governors failed to make an appointment.

They readvertised in October; the outgoing head applied, was interviewed, and, “to the delight of parents, governors, staff and pupils”, was reappointed. “I believe this is quite unique,” our letter said, “and runs contrary to the current stampede from headship.”

There was a postscript. “I have not told the boss that I am sending this letter as he would probably throttle me, but I believe that his story is worth reporting, if only to give heart to young teachers.”

The head in question is Alan Smith, a big 52-year-old with a craggy face and a finger-crushing handshake. The school is Mill Hill primary, in the heart of a big 1960s housing estate on the southern edge of Sunderland. It has 550 pupils, one in three of them claiming free school meals; “a real cross-section of society”.

Even from the outside, though, there’s a sense of something different at Mill Hill - big playing fields, unvandalised, undamaged cherry trees, immaculate flower beds. This is a community that respects its school.

Alan Smith confirms this impression. “The support we get is fantastic - super LEA, super parents, super staff, super children,” he says. Once inside, you begin to get a sense of how the school has earned that support. The corridors and classrooms are full of images of busy, laughing children. Mr Smith shows you the digital camera that produces them, calling it “the best pound;500 we ever spent. Within an hour, you’ve got brilliant pictures. Within a day they’re in the Sunderland Echo. Look what fun they’re having. We like the place to be full of fun.”

As you walk round, he makes introductions - the deputy head, a technician, a cleaner, a former pupil now a teacher, a couple of parents, the site supervisor. Almost always, there’s a whispered comment, by way of explanation: “She’s a star.”

He uses the phrase eight times in less than eight minutes. A Year 2 class crosses the hall on the way to their classroom and he holds the door as the line goes through. Unprompted, one by one, they thank him. “Great children,” he says. “We’re lucky.”

What about those 18 years, then? “Fantastic,” he says (another favourite word). It was his first headship, a Sunderland man coming home to his roots. “I was lucky. The school just grew. We got a great new block - new classrooms, offices, an entrance hall. New staffroom, too. Come and see it.”

There’s a coffee machine, armchairs, microwaves, thre toasters, a dishwasher. “We take good care of them,” says Mr Smith. “The staff, I mean. They’re far and away our most valuable resource.”

But, after 18 years, he reckoned it was time to go. “The school was on a high. We’d had an ‘excellent’ from Ofsted. They deserved a change. There were other things to do.”

Was the CEA job a mistake, then? There’s an uncharacteristic silence. “No. I enjoyed it. I got good vibes out of it. I was working with excellent people. But I missed the school. I felt as though I’d lost my family.”

And he concedes that, although he supports performance management and the threshold system (“If it rewards teachers for doing a good job, I’m all in favour”), it didn’t have the easiest of launches. Much of the system was on hold in that first term, pending analysis of the National Union of Teachers’ court action, and the bureaucracy was growing.

“Let’s face it, it’s a massively contorted way of coming to a very obvious conclusion,” he says.

It wasn’t easy, though, three months after a wonderful leaving party at the county cricket ground, and just two months into a major new job, to ask for his old one back. He had to go through the full application procedure, and was interviewed against three other shortlisted candidates.

Mr Smith took a salary cut, too. As a “new head”, he had to be paid two points below the top of the permitted range. The consolation came in the reaction of his former colleagues and pupils.

His deputy, Sally Davey, who for that term was acting head, describes it. “No, I didn’t write the letter, but I wish I’d thought of it,” she says. “We were so pleased - pleased and relieved. I’d only been deputy for a year; without the support and advice of colleagues, that term would have been a struggle.

“But everyone helped me - and that comes from Alan Smith. He really has built the school so that everyone pulls together. And when we gave children the letter for their parents, the excitement was infectious. ‘Brilliant,’ they shouted. ‘Class! Mr Smith is coming back’.”

Mr Smith himself is more circumspect. Yes, he says, he was conscious of a lot of unspoken staff support. “They weren’t unhappy”.

Parents were relieved, too. “There were lots of pleasant vibes from them,” he says, adding that the governors were, as always, “superbly supportive”.

It is about his own feelings, though, that he speaks most easily. “I used to believe that the only things you regretted were the things you never tried. But I loved every single day of this school - still do. The older you get, the more you realise that every day is special. Walking away from it made me realise how much it meant to me - and I nearly lost it.”

So now there are new targets, new ambitions, new challenges. There’s a new sports hall to be campaigned for, possibly another Ofsted inspection to get through. There’s even an imminent visit from the school’s threshold assessor - a reminder to everyone, Mr Smith says, of how special Mill Hill’s teachers are.

There is a new resolution, too: to warn of teacher overload, yet at the same time to beat the drum for teaching, “surely, the best career of all”. Not to mention the small matter of the identity of the mole. “I’d love to know who it was. Do you know what I’d do, if I found out? I’d throttle him.” And he laughs so loudly that a class nearby falls silent.