How does teachers' technological pedagogical content knowledge (TPACK) inform their instructional planning? How can this knowledge be enhanced? In an interpretivist study of experienced secondary social studies teachers' planning, we sought to discover clues to the nature and development of these teachers' TPACK-in-action as it was expressed in their planning processes. Comparisons of interview data and planning products before and after engaging in professional development that addressed content-focused, TPACK-based learning activity types (Harris & Hofer, 2009) revealed three primary findings, each supported by participating teachers' oral and written reflections upon their learning. The participating teachers' (a) selection and use of learning activities and technologies became more conscious, strategic, and varied; (b) instructional planning became more student-centered, focusing primarily upon students' intellectual, rather than affective, engagement; and (c) quality standards for technology integration were raised, resulting in deliberate decisions for more judicious educational technology use. (Contains 1 figure and 3 tables.)