The regression discontinuity design (RDD) has the potential to yield findings with causal validity approaching that of the randomized controlled trial (RCT). However, Schochet (2008a) estimated that, on average, an RDD study of an education intervention would need to include three to four times as many schools or students as an RCT to produce…

When solving basic number fact problems (e.g., 4x5=20), students with mathematical learning disabilities (MLDs) make qualitatively different kinds of errors than both typically achieving and low-achieving students. This study explores the origin of these qualitative differences through a detailed analysis of one student with an MLD. Data were…

Within the Response-to-Intervention framework, students who fail to profit from high-quality general education instruction, accommodations, and supplemental instruction progress to a more intensive intervention program, sometimes referred to as "Tier III." This article describes a problem-solving approach to designing such intensive, data-based,…