The government has been criticised over its decision to include the English baccalaureate in league tables due to be published this week.
Ron Munson, headteacher at Taverham High School in Norwich, told the Guardian: "I really do not understand what the government is doing. And why is it doing it retrospectively, without having carried out any consultation, and without having published detailed plans beforehand?"
"The fact that they've done it retrospectively is just crazy. We are talking about a qualification that we knew nothing about, and yet we are being measured against it."
He suggested there is a danger that schools will start forcing students to take certain subjects.
To qualify for the English baccalaureate, students need to achieve five GCSE A* to C-grade passes in subjects such as science and maths.
The government's recent education white paper entitled The Importance of Teaching, also set out to improve discipline in the classroom and trial a new approach to pupil exclusions.