This article discusses the value and feasibility of carrying out evaluation research on teacher development and uses as points of reference the author's experiences in two countries, Sri Lanka and Mexico. In Sri Lanka, an evaluation study was designed to understand the effectiveness and costs of teacher development at the elementary level linking teacher preparation with classroom practice and student achievement. The study also evaluated costs and analyzed the possible impact of the results for future policy. The study in Mexico illustrates the challenges of doing evaluation research in an environment dominated by a central state and teacher union politics, and where systemic empirical research on teacher development has been rare. It constituted an initial attempt at looking at the content and the anticipated effects across different approaches to teacher development in Mexico. New calls for greater accountability and better understanding of the reach and limitations of general education worldwide are prompting systems to examine teacher development program effectiveness. In this analytical article, the author discusses strategies and possibilities in the emerging field of teacher development program evaluation.