This paper outlines a theoretical framework which offers an explanation of the complexity of how teachers define their effectiveness in relation to their classroom practice. The research from which this framework emerged was a two-year, mixed method study of 81 primary and secondary school teachers. The use of repertory grid interviews combined with a number of other methods is unique in a study of teachers' practice and, from the elicited constructs, seven key themes emerged. These themes, analysed in relation to three broad career phases, indicate a number of issues important for teachers as they transfer from early- to late-career.