Speaking at the Association of Teachers and Lecturers (ATL) annual conference, members warned that the government's education reforms are ill-conceived. Delegates passed a motion to start a campaign to keep the school leaving age at 16.
Union members will also lobby for the reintroduction of technical schools specialising in vocational education, as an alternative to expanding the academies programme.
Phil Whalley, a teacher from Hardenhuish School in Wiltshire said raising the school leaving age deprives pupils' their freedom of choice.
He said: "Instead of this repressive, negative policy of compulsion, pupils and parents should make the decison for themselves."
Mary Bousted, general secretary of ATL, told CYP Now that young people should not have to decide between a vocational or academic route at 14.
She said: "Most young people will have some good vocational skills and some good academic skills. Why should they asked to turn their back on one or the other?"
She also warned that there are too many qualifications for young people to choose from.
She said: "As long as you have GCSEs and A levels in their current form it will be difficult to persuade young people to do the diploma. The take-up of the diploma has been limited in the first year, but the issues were always foreseeable."
