Prize views of secret garden
His previous works include The House, a behind-the-scenes look at the Royal Opera House that set a trend for documentaries covering whole institutions.
But the real roots of Teachers' TV lie in his 1991 series Culloden, which followed a year in the life of a progressive primary school in east London.
Mr Bethell said: "It was a really honest view of that kind of teaching, and there were a lot of teachers saying, 'At last, someone's recorded what we do.'"
The programme soon caught the interest of the tabloids, which tested some of the pupils in a bid to show that standards had fallen.
"At that point, it became a political football," Mr Bethell said.
"I don't regret the programme, but I deeply regret the impact it had on teachers in the school. I know many of them felt they never recovered."
Mr Bethell, 59, made the leap from teaching to television when he was 40 after friends in the City offered him financial help to set up his production company Double Exposure.
The first programme he produced was about his father's experiences in Italy during the Second World War. His father stayed in the army after the war, moving between postings in countries including Malaya, Germany and Cyprus.
The young Andrew was sent to board at Sherbourne public school, where he was a contemporary of the actor Jeremy Irons.
Mr Bethell went on to study at Toronto university and worked briefly with a Canadian television channel. However, after reading the books How children fail by John Holt and Risinghill: Death of a comprehensive school by Leila Berg, he underwent an almost overnight political conversion and became set on working in an English comprehensive.
He described his first steps in teaching, at Tulse Hill school - then one of the toughest in London - as a "very, very interesting culture shock".
But his height - he is 6feet 7inches - and his rugby player's build made him an intimidating presence in the corridors.
He then spent the next 17 years teaching English in London comprehensives, mostly at Clissold Park, which his children later attended after it became Stoke Newington school.
A keen photographer, director and writer, he was involved in the development of media studies and still gets royalties from some of his books and plays, including a theatrical adaptation of the film Gregory's Girl which has sold a quarter of a million copies.
Although his documentaries won several awards, competition from production companies such as Endemol, the makers of the reality TV show Big Brother, meant that by 2003 he was considering a return to teaching. But then, the night before he was due to go on holiday he received a call asking him if he was interested in a new government-funded channel devoted to teachers.
On a beach in Spain, he began drawing up a six-page, sangria-stained plan for the station.
"We always said it would allow you to see into other people's classrooms because there are usually very few occasions when you can do that," he said.
"For most of us, teaching is a lonely business."