Interest in the regression discontinuity (RD) design as an alternative to randomized control trials (RCTs) has grown in recent years. There is little practical guidance, however, on conditions that would lead to a successful RD evaluation or the utility of studies with underpowered RD designs. This article describes the use of RD design to evaluate the impact of a supplemental algebra-readiness curriculum, "Transition to Algebra", on students' mathematics outcomes. Lessons learned highlight the need for evaluators to understand important data requirements for strong RD evaluation studies, the need to collaborate with informed and committed partners to ensure successful RD design implementation, the value of embedding an RCT within an RD design whenever possible, and the need for caution when contemplating an RD design with a small sample. Underpowered RD studies--unlike underpowered RCTs--may not produce useful evaluation results, particularly if other RD data requirements are not met.