The National Association of Head Teachers said courses based on AS-level general studies should be part of a compulsory package of studies for all 16 to 19-year-olds.
The proposed package, part of the NAHT's response to the Government's consultation on the future of qualifications for 16 to 19-year-olds, also includes compulsory units in communications, numeracy, computer skills and personal and social education.
Under the NAHT proposals, students would have to complete at least two A-levels and one AS-level, as well as compulsory general studies and key skills courses, to gain the leaving certificate.
But there would be optional packages of up to three A-levels and two AS-levels, or their vocational equivalents, for the most able.
The heads argue that voluntary schemes designed to encourage institutions to take a wide range of A and AS-levels would fail.
NAHT general secretary David Hart said: "The post-16 programme of study is excessively narrow. It is outdated and unfit to meet the challenges to this country."
The consultation, which ended on December 18, produced 1,920 responses, Department for Education and Employment officials said.