Does teacher professional development make a difference? How do we know? While researchers and policy-makers acknowledge that teacher professional development (PD) needs to be assessed and evaluated, there is often little clarity as to how this can be achieved. Evaluation of teacher PD by schools has been described as the weak link in the PD chain despite it being linked with improved PD experiences and pupil outcomes. A lack of skills and tools to carry out such evaluations may be contributing to this or indeed it may be linked to how PD is conceptualized. This article explores extant literature and models of evaluation revealing gaps in existing evaluation frameworks. Resulting from this a provisional PD evaluation framework was developed for use in a study that set out to formally evaluate the impact of a PD initiative on teachers' professional learning in five urban primary disadvantaged schools in the Republic of Ireland. Following application within this study, the framework was critiqued and revised. This resulted in a new PD Impact Evaluation Framework that may support teachers, schools, departments and policy-makers to carry out systematic and focused evaluations of teacher PD.