This empirical study examined teachers' competencies in school-based assessment in Design and Technology, which is an important subject for Singaporean low-achieving (i.e., Normal Technical) secondary school students. The current school-based assessment in Design and Technology in Singaporean secondary schools consists of three performance tasks: (1) design journal, (2) presentation board, and (3) design artifact. As students' performances on these tasks are assessed for accountability demands, teachers' competencies in designing and implementing high-quality performance tasks as well as in judging the quality of student work are of paramount importance. Our observation of the current school-based assessment practice in Design and Technology is that the teachers have blindly followed the standards and moderation procedures designated by the examination board. The purpose of this study was threefold: (1) To understand teachers' competencies in designing and implementing school-based assessment for Design and Technology, (2) To examine the relationship between the quality of performance tasks and the quality of students' work in the school-based assessment, and (3) To understand teachers' competencies in judging and moderating the quality of students' work in the school-based assessment. The sources of data included teachers' interviews and artifact analyses. The participating teachers in the study taught Design and Technology in a low-achieving school and were interviewed for their competencies in designing and implementing school-based assessment for design and technology as well as in judging and moderating quality of students' work. They were also asked to share their views of the moderation procedures set by the external examination board. The performance tasks designed by the participating teachers and their corresponding student work samples were analysed using the criteria for authentic intellectual quality. The interview data reveal that the teachers were concerned about their competencies in using rubrics to judge the quality of students' work in school-based assessment. They also felt that their competencies in school-based assessment and moderation practices could be improved by professional development. The performance tasks in the school-based assessment for Design and Technology were found to be of low authentic intellectual quality because of a heavy focus on drill-and-practice of factual and procedural knowledge. As a result, the corresponding students' work samples were also of low authentic intellectual quality. The implications of these findings on the design and planning of professional development programmes in school-based assessment for Design and Technology teachers will be discussed in the full paper.