Multitiered systems of reading instruction and intervention, including response to intervention, are widely used in early reading by schools to provide more intense services to students who need them. Research using randomized controlled trials has compared innovative Tier 2 interventions to business-as-usual Tier 2 approaches and established a number of important components that compose effective Tier 2 interventions in early reading. The purpose of this study was to test the impact of a Tier 2 intervention with Tier 2 compared to Tier 1 instruction alone using regression discontinuity. A cut score was used to assign first-grade students at risk for reading difficulties to Tier 2 intervention plus Tier 1 instruction. Students who missed the cut score in the control group received Tier 1 instruction only. Students in the treatment group, just below the cut score, made greater gains on the SAT10 total score and the individual subtests than students just above the cut score. Outcomes were not significant on oral reading fluency.