Education experts argue that using rich mathematical tasks in student-centered classrooms is especially conducive to student learning (NCTM 2000). That said, they also acknowledge that using complex tasks and developing student-centered classrooms can be intimidating and challenging for teachers (Chazan and Ball 1999). One difficulty associated with using complex tasks is ensuring that high levels of cognitive demand are maintained throughout the lesson while engaging every learner. However, if these types of difficulties are bridged, teachers' critical reflection of their students' thinking and their own actions can potentially allow them to tailor instruction that will help students make sense of mathematics. Teaching via problem solving has been shown to be an effective way of engaging students in learning with understanding. This participatory pedagogy allows the teacher to enable rich mathematical discussions that originate from working on challenging problems whose solutions provide a launching pad for deeper explorations. Learning and teaching via problem solving differ from the traditional teacher-led approaches in the areas of the teacher's and the students' roles. In this article the authors share how being reflective on their practice has aided their growth and enabled them to be responsive to students' learning. They discuss their interactions with preservice elementary teachers during a unit on fractions.