This article reports on two approaches to teacher professional learning in which the use of challenging tasks was the focus. In the first case, two full days of professional learning were followed by the opportunity to teach up to ten challenging tasks. In the second case, teachers observed three lessons built around challenging tasks taught by members of the project team. This article describes the professional learning approaches, illustrates the kinds of tasks involved, and discusses similarities and differences in the data within and between the two groups of teachers. It also discusses affordances and limitations of the two professional learning approaches.