The term differentiation has been widely used within education. This study makes use of the author's professional experience and a literature review to present a model of differentiation in practice; it seeks to suggest ways in which teachers' skills can be enhanced. The study aims to give an understanding of how teachers differentiate; what that say they do; and what can be described as good practice. Together with the wide ranging review of the literature, it draws upon field research, interviews, questionnaires, an analysis of OfSTED inspection reports and the author's experiences of running staff development courses on differentiation. It also includes work published by the author. The study is an original presentation of a comprehensive review about differentiation from the perspectives of the literature and serving teachers and contributes to the debate upon the methodological approaches to the study of the development of teaching skills. Conclusions are offered based upon an analysis and a discussion of these sources.