This article reports findings from a multi-year study of teachers' conceptual change coincident with the development of instructional expertise among teachers involved in educational reform efforts in schools in Santiago, Chile. Conceptual change in teachers is important because recent research indicates that students of teachers who function at more complex conceptual levels tend to achieve significantly higher achievement test scores, and cognitively complex teachers and teacher leaders tend to implement more educational reforms and to more effectively mentor other teachers. Given the current emphasis on teacher leadership in developing schools as learning communities, research identifying and describing mechanisms to develop and mentor teachers is important. The findings show that while no changes in levels of reflection were found, small changes were evident in reflective dialogue comments by the four teachers studied. In addition, the researchers identified implications for educational leaders interested in mentoring teachers engaged in reflective dialogue about their practices and concluded that the assessment standards appear to be both useable and to have construct validity in assessing reflection. (Contains 1 figure and 1 table.)