When Martin Lawrence was a primary teacher, he took a group of pupils to a running track. It had just rained and worms were wriggling out of the ground.
"Some pupils hadn't seen a worm before. To see their faces - it was so rewarding. Now I get to do that sort of thing daily," he said.
Mr Lawrence left Grove Vale primary in Southwark, south London, in 1994 to work part-time as a learning officer at the Natural History Museum. He organises workshops, writes activity sheets for schools and is responsible for part of the museum's website.
Mr Lawrence, now 38, continued to work as a supply teacher for a while but left the profession in 2001. "Working in a primary school is a very hard job, particularly in terms of class sizes and the resources available," he said.
Those thinking of following him out of teaching can now consult a new guide written by ex-teacher Catherine Maguire, a careers adviser at London Metropolitan university. In it, she considers why teachers quit and advises them on their options.
Ms Maguire, 31, said: "People leave because of the stress of being on show constantly, they feel they can't have an off day. Mounting paperwork and constant changes in educational policy are also mentioned. A few people also say the status of teachers and discipline were factors in leaving."
A study by Professor Alan Smithers and Pamela Robinson for the Department for Education and Skills found that the main reason teachers left was workload and the need for a new challenge.
They estimate that about 8 per cent of teachers left state schools in 2002, including those retiring or leaving to bring up a family. About 5 per cent left for jobs outside education and 4 per cent took other educational posts. Ms Maguire interviewed 35 people. Most, like Mr Lawrence, stayed in education. But others moved to jobs from translating to auditing.
Mr Lawrence has an environmental science degree. He finished his postgraduate certificate in education in 1991, but soon realised he wanted to focus on environmental education.
"I was doing after-school clubs, too, and it was very rewarding, but it was not enough. When I saw the job at the museum advertised in The TES, I jumped at it," he said.
Ms Maguire believes it is important to think about transferable skills, but said: "Put them in context. Saying you would make a good manager (of adults) because you have managed a class of 30 15-year-olds is not enough."
She tells people thinking of a change to identify what they like about teaching - and how they could incorporate that into a new job.
Ms Maguire notes the mixed feelings of some who quit. "One said to me 'you don't get the same lows outside teaching, but you don't get the same highs either'."
"What can I do with a teaching qualification?" will be published in the spring by Trotman, pound;11.99