The purpose of this article was twofold: (1) to explore the feasibility of the regression discontinuity design (RDD) in response-to-intervention implementation research and (2) to expand upon the limited research on vocabulary instruction for kindergarten students who are at risk for reading failure due to limited vocabularies. This pilot study employed an abbreviated, prototypical tiered instructional model to deliver vocabulary instruction to both at-risk kindergarten students and students not at risk for reading failure. The study was designed using RDD and the data were analyzed using a regression-based analytic model. The pros and cons of this research design, specifically in regards to learning disabilities research, is examined.