Numerous studies, including our own, have documented that teacher noticing interventions can be effective in developing teachers' abilities to notice salient aspects of the mathematics classroom. In this study, we explore how specific aspects of one such intervention may have supported three prospective teachers in learning to notice high-potential instances of student mathematical thinking. The findings provide evidence that it was not one particular aspect of the intervention that was effective in supporting their noticing, but a combination of factors that include the use of a noticing framework, interactions with their peers and a facilitator, and targeted learning-to-notice activities. [For complete proceedings, see ED581294.]