Abstract
In spite of the preponderance of in-service education programmes in Nigeria, no noticeable impact has been recorded in terms of actual improvement in the quality of secondary school biology teaching. The purpose of this study therefore was to ascertain the effect of a Constructivist-based in-service model on secondary school biology teachers’ pedagogic content knowledge (PCK). The study which employed the posttest-only control group experimental design investigated seven dimensions of the teachers’ pedagogic content knowledge. The subjects comprised 80 biology teachers in Imo state. The mean, standard deviation and t-test were employed to analyse the data. The result revealed that the Constructivist-based in-service model was effective in improving the secondary school biology teachers’ PCK in all the seven dimensions.