The M.Teach course is based in the school, with tutors from the Institute of Education in London visiting its 17 participating teachers several times a term.
John Fairhurst, Shenfield's head, set up the programme as both a professional development and recruitment and retention tool.
The teachers following the course have two-thirds of their fees paid over three years, and the shortfall is paid if they stay on for a fourth year.
Mr Fairhurst said: "When I mention the possibility of doing a masters to applicants at interview, their eyes usually light up, and they are the kind of teachers we want in the school.
"They know it means extra work, but the way we have arranged it means there is no travelling, so no time is wasted."
Teachers of all ages are taking the course, basing their written projects around work they are doing in school. For example, the gifted and talented co-ordinator is writing a dissertation on gifted and talented provision.
Zoe Moss, 28, course leader in accounting at Shenfield, took up the course after her NQT year, 18 months ago. Her dissertation will be based on a project she is leading to improve the school's vocational provision. "I already have a masters in research and it felt quite natural to move to the masters in teaching," she said. "I'm the sort of person who really likes to keep learning, and when I finished my PGCE there wasn't much left. This keeps me reflective about my teaching and gives me a marketable qualification at the end."
She said that the workload was manageable, with occasional pressure when deadlines loom. "It's extra work, but at the end of the day you gain a qualification," she said.
Mr Fairhurst said the aim of the programme was to create better skills and more reflective teachers.
"If we mean what we say about a lifelong attitude to learning, teachers should be the role model for that," he said. "It is probably most useful for the younger teachers, as they are still moulding their teaching."
Photograph: Teri Pengilley.