This paper focuses on the development and study of a framework to provide direction and guidance for practicing teachers in using a web-based case studies program for professional development in early reading; the program is called Case Studies Reading Lessons (CSRL). The framework directs and guides teachers' analysis of reading instruction by focusing their attention to three critical dimensions of the process of teaching; in theory, analysis of a wide variety of reading lessons, using this framework, should contribute to teachers' expertise. We report on a study of the Thinking Questions, which scaffold teachers' analysis of the reading lessons, to determine the extent to which their responses meet theoretical expectations. Results suggest that teachers' ratings of lessons tap their overall expertise in analysis of reading instruction, such that the three dimensions and features that represent these do not constitute separate factors. However, performance on the Thinking Questions differentiated more and less experienced teachers. As expected, less experienced teachers wrote longer and more specific comments about the instruction than more experienced teachers, who tended to highlight effective principles. The results suggest that an analytic framework of the kind used in CSRL holds promise as an effective component of a case-based professional development program. However, they also point to the need for further study of the framework and its influence on teachers' own teaching practices.