Evidence shows that teachers make a critically important contribution to school and system improvement. Teachers are pivotal in generating and sustaining changes that impact directly upon learning and learners. Their positive influence is further enhanced when they engage in collaborative professional learning with the prime aim of generating new ideas, new strategies and new approaches that will make a positive difference in the classroom. While there are many approaches to collaborative professional learning, some models are more successful than others. Within the most effective models, placing impact at the heart of professional collaboration and learning is key. If learners, teachers, and the school are to directly benefit from collaborative professional learning, it is important that gauging and assessing impact is a core component of the collaborative model or approach.