In this thesis the author sketch the development in the early 1990s of the Mayer key competencies in Australia and the author compare them with other notions of work-related skills developed internationally at about the same time. The author focuses on the ambitious assessment proposals of the Mayer committee and the different views and arguments that were made about those proposals. Having reviewed the key competencies debate, the author analyse notions of competence and ability and distinguish the generic Mayer competencies from other ideas of competence and competencies. As a result of this analysis the author argue that the Mayer key competencies must be seen as generic abilities rather than specific competencies. The author also argue that the key competencies are not achievements but rather that they are best thought of as aptitudes that predict abilities to learn new things. The author consider 100 years of research in psychometrics and cognitive psychology about generic abilities with particular attention to the work of Gardner, Sternberg, Carroll and Ceci. As a result of this analysis the author sketch a model of cognitive abilities within an overarching model of performance. The author then turn from the theoretical and research literature on generic abilities to consider what happened to the assessment proposals that were referred by the Mayer committee to the curriculum and assessment authorities in the various states and territories of Australia. The author undertook reviews of key competencies assessment issues for the commonwealth and the Victorian governments in 1996, and in that work the author proposed a regime for school-based assessment of levels of performance on the key competencies. With commonwealth government support this proposal was trialled in 10 secondary schools with 110 teachers assessing 350 year 11 students in 1997. The aim of the trial was to have students separately assessed by groups of teachers to see what degree of agreement there was between different teachers from different subject areas. Through this trial the author developed the notion of whole- school assessment in which all the teachers of a student contribute to a single, integrated report on the generic abilities of a student. In the trial the author conceptualised and implemented a cost-effective method of producing a collective view of a student from all the teachers of that student. The assessment trial showed that teachers could in most cases make global, impression judgements of key competencies performances with no more that three minutes formal reflection per student. The judgements made by different teachers were quite consistent with each other, and as a result they can be validly and reliably used to develop an overall report for a student. The teachers participating in the trial judged the assessment procedures to be efficient and cost-effective. Analysis of the assessments of teachers participating in the trial shows that pairs of teachers (from any combination of subject areas) typically produce an acceptable level of agreement in about 90 percent of cases. The further work the author has done on the whole-school assessment of key competences has demonstrated on three other occasions that the assessment process the author has developed is practical and useful.