GeoThentic, an online teaching and learning environment, focuses on engaging teachers and learners in solving real-world geography problems through use of geospatial technologies. The design of GeoThentic is grounded on the technology, pedagogy, and content knowledge (TPACK) framework as a metacognitive tool. This paper describes how the TPACK framework has informed the authors' design endeavors and how a set of assessment models within GeoThentic can be used to assess teachers' TPACK. (Contains 1 table and 10 figures.)