The number of candidates seeking and completing online courses and programs in teacher education continues to increase in order to meet the licensing flexibility demands of adults pursuing teacher certification. Using the theoretical constructs of learner-centered instruction and zones of proximal development, this paper provides an overview of the design principles, analysis of qualitative evaluation data, and description of the refinement of an asynchronous online mathematics pedagogy course for graduate students seeking a teaching license in elementary education (children ages 5-12). Inductive qualitative analysis indicated that course revisions led to an increase in the frequency of teacher candidates' high-level tasks and quality lesson plans. Implications for the design and refinement of online teacher education courses are also shared.