The study was conducted in the Mpumalanga province and focused on a sample of 18 externally evaluated underperforming secondary schools across all four districts of the province. The schools obtained an average pass rate of less than 30% in the 2011 Grade 12 examinations. The main objectives of the study were to analyse the purpose of whole-school evaluation (WSE) from a quality assurance perspective; to investigate the significance of a key component of WSE, namely assessing the quality of teaching, learning and educator development; to analyse the Grade 12 results of externally evaluated underperforming secondary schools pre- and post-evaluation; to analyse monitoring and evaluation reports for changes in teaching, learning and teacher development, as well as to identify factors impeding teaching, learning and teacher development in underperforming secondary schools. WSE is a system of evaluating the performance of schools as a whole. Corporate contribution to improve performance is measured, rather than simply the performance of individual staff members. Furthermore, WSE is one intervention to move schools that are in a critical situation along the path to becoming effective schools. Guidelines for quality assurance in education, especially at school level, are underpinned by the nine areas for evaluation (AFEs), namely basic functionality of the school (AFE1), leadership, management and communication (AFE2), governance and relationships (AFE3), quality of teaching and learning, and educator development (AFE4), curriculum provisioning and resources (AFE5), learner achievement (AFE6), school safety, security and discipline (AFE7), school infrastructure (AFE8), and parents and the community (AFE9). The mixed methods approach was used. This approach made it easy to reconcile findings through triangulation and complementing qualitative and quantitative data (both primary and secondary). The study relied on secondary data (external WSE reports and Grade 12 results), as well as primary data obtained from questionnaires administered to school management teams (SMTs) of the sampled underperforming secondary schools. The study revealed the great level of acceptance of the external WSE process by SMTs in Mpumalanga province’s underperforming secondary schools, as a means of quality assurance in order to achieve improvement. Furthermore, it revealed the extent to which improvement and development in the underperforming schools occurred as a result of the external WSE process. It was found that the results of seventeen of the 18 schools (94.4%) had improved. Furthermore, the study confi rmed that what was revealed in the external WSE as areas for development came as a revelation to SMTs. As a result, the manner in which teaching, learning and teacher development (AFE4) as a key component of WSE is viewed by teachers and SMTs, has been positively influenced.