This study (a) assessed the influence of an integrated nature of science (NOS) instructional intervention on inservice secondary science teachers' understandings, retention of those understandings, and their NOS instructional planning and practices; and (b) examined factors that mediated the translation of teachers' NOS understandings into practice. Nineteen teachers participated in an intensive, 6-week NOS course, which concluded with teachers developing plans to address NOS in their classrooms. Next, 6 participants were observed as they implemented their instructional plans. Data sources included pretest, posttest, and delayed-test NOS assessments, classroom observations, and several teacher-generated artifacts. The NOS course was effective in helping teachers develop informed NOS conceptions and retain those understandings 5 months after its conclusion. Teachers met with challenges and successes as they attempted to address NOS instructionally. The translation of NOS conceptions into practice was "primarily" mediated by the very nature of teachers' newly acquired NOS understandings, which were "situated" within the science contents, contexts, and experiences in which they were developed (i.e. the NOS course); thus, limiting participants' abilities to transfer their understandings into novel contexts and contents. The results helped build a model of the sources of science teachers' pedagogical content knowledge for teaching about NOS in content-rich contexts.