With the pressure to improve student achievement, and the propensity to use PD to influence instruction, it is easy to overlook the complex process of teacher learning. The Vygotsky Space represents iterative learning within public and private dimensions, where teacher knowledge building is positioned as interactive cultural events situated within social practices. Three cases of teacher learning are synthesized into a multiple-holistic case study using cross-case analysis as a way to explicate the Vygotsky Space as a tool for understanding non-linear learning over time. The Vygotsky Space is applied as an analytical model to illustrate the relationship between the public discourse that occurs between colleagues and the subsequent private appropriation of ideas and transformation of an individual's repertoire of practice.