Abstract: This study reports the alternative conceptions that were exposed by high school learners on some concepts on limits and trigonometry. The alternative conceptions were discussed at a day-long teacher professional development work-shop organized for high school teachers teaching in Nyanga district, Zimbabwe. The deliberations of the workshop were videotaped in order to allow replays during data interpretation. The sixteen teachers who attended the workshop held different conceptions on the nature of mathematical knowledge and skills which influenced their assessment of the learners’ alternative conceptions. However, the teachers concurred on the interpretations and professional insights that they developed from the learners’ alternative conceptions. The use of baseline-test performance to inform teaching practice is presented as an effective way of diagnosing learners’ prior knowledge that teachers can use to facilitate learners’ development of new concepts.

Key words: Alternative conceptions; Prior Knowledge; Conceptions; Formative assessment