The Assistant Masters' Association (AAM) was a trade union representing male teachers in British secondary schools. The union was founded in 1891 as the Incorporated Association of Assistant Masters in Secondary Schools, although it soon became the "Assistant Masters' Association", a counterpart to the Association of Assistant Mistresses (AAM). Membership of the union grew steadily, reaching 3,259 in 1910, and about 40,000 by 1978. From 1978, single-sex trade unions were prohibited, and the AMA accordingly merged with the AAM, forming the Assistant Masters' and Mistresses' Association.