No matter how one formally define response to intervention (RTI), most definitions contain common components: scientific, research-based instruction; the use of learning rate and level as the basis for determining effectiveness of intervention; and decisions about intensity and duration of interventions based on a student's response to interventions across multiple tiers of service. The St. Croix River Education District, which manages special education services for five school districts in east-central Minnesota, has been involved in implementing these components for the past 20 years, though no one knew it as Response to Intervention back then. In this article, the author describes the RTI model adopted by the St. Croix River Education District and the evaluation method it used for assessing the effectiveness of RTI.