Teachers who branch out and supplement their income by writing textbooks are by no means uncommon in the profession. Some get the publishing bug in a big way, and switch careers from school to educational publishing house - and sometimes back again.
The experience of such teachers is that the skills they have mastered while working in a school stand them in good stead in a commercial environment, and the move can be extremely rewarding.
Chris Dunning, a dedicated biology teacher for many years, spent three years in educational publishing after taking early retirement.
He is now teaching biology again, this time in an independent school (after a publishing take-over made commuting impossible), but views his publishing stint "almost like a sabbatical. It has broadened me, enhanced my awareness of pedagogical issues, and given me the opportunity to talk to some of the most authoritative science educators in the country."
He began teaching at a large Bristol comprehensive in 1970. "I never liked the day-to-day grind of marking and preparation, but I did like the opportunity to be involved in your own subject area and present things in an interesting and fun way. The Seventies were a time of great curriculum development, and there was a lot of freedom to devise quite exciting curriculum materials; almost everyone I knew was involved in developing things."
He later became head of science at a Reading comprehensive. After 17 years, he began to feel he might "dry up" if he stayed any longer. He took early retirement - only to join Nelson publishers as a secondary science editor.
"The ideal thing about publishing, for a teacher, is that you can bring your own subject knowledge and teaching experience to bear on the job, and that gives you a bit more authenticity.
"Teachers also have many skills they don't realise they have, which are easily transferable to a commercial environment: management, interpersonal and communication skills - putting ideas across, presenting and running meetings.
"Teachers can graft on the publishing skills, whereas I'm not so sure that publishers could move into the classroom," he says.
Some teachers find much earlier in their careers that, despite a love of their subjct, they are better suited to publishing.
Nadezda Poole, now 27, spent two years teaching geography at a comprehensive in Crawley, but left "because I felt I wasn't making a difference, the challenges hadbecome the challenges I didn't want - like can you get this class to be quiet?" Since September last year she has been working as a marketing executive at Hodder amp; Stoughton Educational. "The advantage of teaching experience - and there are quite a few ex-teachers at Hodder - is that you know which books are going to work, and which aren't.
"You also know what teachers are looking for in terms of building teaching aids into textbooks. I still get fired up looking through geography books and thinking, 'That would be excellent in class'- but I wouldn't go back into teaching, because of everything else that goes with it."
Tony Mullen enjoyed his eight years' teaching geography and PE, but decided in his 30s that it was time for a change.
He joined Folens educational publishers as a commissioning editor; worked at Ginn on its secondary science scheme; and then moved to the BBC, where he is now a planner in the schools' programmes department.
"What I took to publishing was a knowledge of how teachers work in the classroom, the demands and pressures , and the resources that teachers find most accessible. I also had a network of contacts."
Sonia Clark, now a publisher for Heinemann's international division, started out as a biology teacher, and later combined and alternated periods of teaching and publishing work.
When her children were young, she gained some copywriting experience and at 40 she applied for her first publishing job, doing project management for Macmillan's African and Caribbean list.
She spent a further five years in full-time teaching, followed by a job as Nelson's senior science editor. She now works for Heinemann and spends 10 to 15 weeks a year travelling to Africa and the Caribbean to talk to authors, education officers and teachers.
"I have found publishing and teaching complementary," she says. "You have an affinity with students and teachers, and a knowledge of their different needs.
"And working in a business environment makes you a more rounded person, gives you more breadth. There are aspects of teaching that I still miss, but I do feel quite privileged to have had a second career."