In order to contribute towards the construction of an empirically-grounded theory of effective continuing professional development (CPD), this paper seeks to develop a model of the effects of teachers' CPD or in-service education and training (INSET). It builds on an earlier typology of INSET outcomes and compares it to two previous classification frameworks. It is argued that the proposed model of outcomes could be used to delineate more clearly the specific effects which might accrue from different CPD formats.