How long should you stay in one school? There’s no easy answer. New teachers often move on after a year - setting up home elsewhere, or leaving early mistakes behind. After that, the quest for promotion, or simply for a different sort of experience, means that over a period of five years most schools will see significant staff changes. Invariably, though, there are one or two fixtures. Typically, a primary school will have a couple of NQTs, two or three teachers with three or four years’ service and one who’s been there more than 20 years.

What makes a teacher or a head stay in one school most of their career? The answer seems to be a case of “if it ain’t broke don’t fix it”. If you’re on top of your job, you get on well with the children, you have good friends in the staffroom and you don’t thirst for promotion or a different part of the world, then it’s easy to see the years pass by. School life, after all, is never boring. Children come and go in all their glorious variety, as do government and local authority initiatives.

Howard Handley, retiring this year after 29 years as head of Laurance Haines primary in Watford, suggests that changes in his own school over the years have provided a stream of new challenges. “The infants and juniors were amalgamated, then we opened a unit for children with specific learning difficulties. The challenges have all been here, as it turns out.” In common with many long-serving teachers, he feels that the educational wheel has come full circle. “When I started, every lesson, every day was written up and advisers came to check that you were thoroughly prepared. Then came the days of greater flexibility and topic teaching, and now the formal side has made a comeback - and it’s not necessarily a bad thing.”

Long-serving secondary science teachers, by contrast, seem to regret that there no longer seems to be enough time for practical work and for pursuing an interesting idea to its conclusion. “In the past, if you studied a topic such as photosynthesis, and the students enjoyed it, you could take another couple of lessons to do some extra work,” says David Goldstein, just coming to the end of 20 years at Wheeler’s Lane school in Birmingham. “You can’t do that now. As a result, the teaching isn’t as enjoyable and the students don’t get the science education they used to.”

John Lawrence, retiring from the chemistry department at Bablake school in Coventry, says much the same. “We cover a lot of topics at A-level, but they tend to be glossed over; we don’t seem to go into the depth that we used to. The amount of time that the modern syllabus leaves for practical work means that the average student leaving school with A-level chemistry has done far less practical work than even 15 years ago.”

Howard Handley and David Goldstein are excellent examples of loyalty and service to a single school, and they’d be the first to acknowledge that there are others with similar records. John Lawrence, however, is surely in a league of his own. In September 1948, he started at Bablake as a pupil. In 1955, he left for Imperial College in London, where he studied chemistry. In 1958, he returned to Bablake as a teacher.

This summer he retired after 43 years’ continuous service to the same department of the same school.

Bablake - a boys’ direct grant grammar for the first 20 years or so of Mr Lawrence’s career, now an independent mixed day school - is a beautiful place in the sunshine. It’s not difficult to imagine someone walking down the drive carrying the details of another job in his pocket and deciding not to apply for it after all. “At one point in our early married life,” says Mr Lawrence, “we did wonder about emigrating to Australia or New Zealand, but we never went further than getting some information.”

He really only came into teaching - and to Bablake in particular - by chance. “It was in my third year at Imperial College,” he says. “I was in Coventry for Christmas and I met Mr Phillpott, head of science, in town one day. He said there was going to be a vacancy and suggested I applied for it.”

Mr Lawrence, who up to that point had been looking at a career in industry, pointed out that he had no teaching qualification - as a graduate you didn’t legally need one then - and wondered whether he should do a diploma first. The reaction, he recalls, was perhaps typical of that time and that kind of school. “Phillpott said, ‘You don’t want to fill your head with all that rubbish’.”

Like Howard Handley, John Lawrence has fed on change within the same school - the abolition of the direct grant system, for example, led the school to become fully independent and to admit girls. How did he feel about that? “If you’d asked me in my early years, before it happened,” he says, “I’d have said I viewed it with horror. But when the time came, we took it in our stride. Now I feel it’s been a blessing. It’s made for, how can I put it, a pleasanter working environment. I know there are statistics that say pupils achieve better in single-sex schools, and here the girls do a little better, but it’s not all that measurable, and there are a lot of social advantages.”

He has strong memories of a more dour, all-male Bablake, under an authoritarian head. “A figure of awe in a black gown that flowed out and filled the corridor so you cringed in the doorway as he went past.” Succeeding heads, wishing to humanise the regime, had to work hard, he recalls, not only to win over old-style teachers, but to build new relationships with pupils who interpreted liberalism as weakness.

Mr Lawrence is an engaging man - quiet, scholarly and, by his own admission, rather shy. Somehow you’re not surprised that he’s a railway enthusiast, and that he ran a model railway society in school for many years. It seems to fit the image. “I never felt headship was for me,” he says. “I’ve always been lacking in self-confidence and I didn’t want the responsibility. Looking back now, though, I know I could have done the job.”

In the end, however, the classroom and laboratory work has given him deep satisfaction. “Teaching doesn’t give you much of a financial reward,” he says. “But it gives you emotional satisfaction. Is that the right word? I suppose it is. You feel you’ve done something for society, and that’s what makes this an enjoyable job.”

He recalls particularly his 30 years as examinations secretary, which meant coming into school in August for the results. “It was good to be able to congratulate the winners and console the losers - to be there with them in their success or, occasionally, failure. It’s just dealing with human beings I suppose, and if you like that, teaching is a good job for you.”

Now he is leaving to enjoy his time with his grandchildren. Or is he? One thing that’s striking about all three of these veterans is that they are reluctant to go away and lie in the long grass. Howard Handley is going to work with student teachers. David Goldstein is to be a laboratory technician in the same school: “That’ll suit me,” he says. “Less responsibility, less work, but still involved.” And John Lawrence? He’s coming back to Bablake in September to sort out and run the school’s archives. And if one day there’s a chemistry teacher off sick, and somebody comes to find him in the archives room, well, as he says, “I wouldn’t be averse to that.”