More than 6,000 charter schools exist in the United States, and of these 120 are Montessori charter schools. When studying charter school practices, researchers often examine issues such as performance accountability measures and effectiveness of charter school curricula. In doing so, the outcomes often overlook the challenges for teachers as they attempt to blend the demands of being a charter school with performance accountability and charter school philosophies, such as the Montessori philosophy. In this longitudinal case study, I examined the ways in which teachers in a charter Montessori school used professional development to help balance the demands for standardized testing performance and Montessori goals. The findings illustrate that significant challenges exist for teachers blending multiple educational goals but that professional development can aid teachers in filling in gaps in their existing curricula. This study encourages (1) researchers to question the ways in teachers can be supported through professional development to meet accountability measures and (2) stakeholders to consider how accountability measures focused solely on student performance can have detrimental effects on charter school curricula implementation and teacher retention.