When ACT secondary colleges opened in 1976 they constituted the first government senior secondary system in Australia to design their own curricula and assess their own students under the general direction of their own college boards and within broad system guidelines. An Accrediting Agency was set up to approve the courses of study devised by the colleges, determine assessment procedures, arrange certification of students' attainments and negotiate acceptance of students' qualifications with tertiary institutions and employers. All but one of Canberra's private schools teaching to senior secondary level also joined this accreditation system. This field study traces the genesis and development of the ACT schools accreditation system, and looks in detail at its implementation at system and college level. Although this study analyses the accreditation system in some detail, it is intended to be descriptive rather than evaluative. Information was obtained mainly from primary sources: official reports; studies and papers written by participants, surveys conducted in the colleges and original documents. Interviews were conducted but were used mainly as a check on written information.