The technology college in the deprived Forest of Dean appeared for the third time in Ofsted's list of outstanding schools. This year 83 per cent of pupils got at least five GCSEs at grades A* to C. Last year the figure was 74 per cent, against a national average of 55 per cent.
Teachers get time to observe each others' lessons, sometimes using a special classroom with a one-way mirror, and are encouraged to do their own research into better teaching or organisation.
Rob Broadbridge, headteacher, said Dene Magna was "run by teachers, for teachers", so work by the English department could potentially benefit children in maths lessons.
"Being absolutely focused upon teaching and learning - that is the crux of it," he said. "Ultimately that will have an impact on elements such as behaviour. When students get into a classroom, they are going to ask themselves if this lesson is worth behaving for."