This paper presents a two-phased, job-embedded, teacher professional development model (TPD) which employs action research and on-the-job professional support. The model is a response to evaluative research evidence which shows that in spite of their pre-service and in- service training, primary teachers’ traditional perspectives of science education persisted as a barrier to effective implementation of primary science curricula reform. The TPD differs from the Cascade model which is widely used in teacher training. That model transmits teacher learning. The TPD is grounded in enquiry and the principles of andragogy. In the case study, using TPD, two teachers were actively engaged in the systematic investigation of their classroom practices, as they taught the Grade 4 science unit of Jamaica’s national primary curriculum. This resulted in shifts in teachers’ approach to classroom assessment in phase 1 and phase 2, a deepening of conceptual understanding, and use of enquiry teaching as intended for the Science unit. The model has relevance for similar educational contexts.