Professional Development Schools (PDS) were intended to be a comprehensive approach to total-school reform targeted toward the effects of poverty and educational disadvantage. This paper examines the processes and contexts found in PDSs and tests how they might be logically and empirically linked to measurable improvements in achievement. The purpose of this article is to put forth a fully articulated model that makes explicit the depth of critical inquiry necessary to produce changes in student achievement, and report the results of a partial application of this model focused on practices known to be associated with student achievement--family involvement in a PDS. This study emphasized the importance of conflict in the Deweyan sense and critical questioning, as well as the role of formative assessment in the analysis of the student work samples. Professional development in the form of inquiry presented an opportunity for expansion of knowledge and skill through a sustained exploration of issues, which is in sharp contrast to the more prevalent model of a single workshop for teachers or presentation by outside experts.