This research project, which was modeled on the constructivist theory of acquiring knowledge, and on recent recommendations regarding classroom instruction, investigated the impact of problem-based teaching and learning (PBTL) on the performance of high school mathematics learners. The effect of an intervention programme on an experimental group of students was compared with a control group by assessing their mathematical knowledge and skills; their procedural proficiency and conceptual development on varied mathematical contents; their skills in managing and controlling learning; and their views towards their learning programmes. The results obtained indicated that the experimental group indicated a higher conceptual understanding, an improved use of procedures, a higher level of managing and controlling learning, and positive views towards the programme and interest in the fundamentals of learning mathematics. An analysis of the data obtained by the on-progress instruments employed for the experimental group also indicated improved quality of participation and reflective thinking practices. Key Terms: Authentic assessment; Cooperative learning; Curriculum; discovery; Mathematical achievement; Mathematical performance; Meta-cognition/Self-regulation; Problem based; Problem solving.