In this article, the authors examine specific learning outcomes—notably, increases in teachers’ knowledge, changes in their practice, and the impact on student achievement—as a result of teachers’ participation in a situative-based, adaptive professional development (PD) program. The findings suggest that participation in the Problem-Solving Cycle (PSC) model of PD can support at least modest improvements in teachers’ knowledge and classroom instruction within a relatively short time frame. This study of the PSC highlights one way to examine the effectiveness of adaptive PD using longitudinal data and quantitative analyses. Based on those analyses, the PSC does appear to have the potential to substantially affect teachers’ knowledge and instruction and, perhaps, their students’ achievement.