Because several studies have investigated student outcomes in schools implementing Response to Intervention (RtI), relatively little research has investigated the impact of implementation on students' long-term achievement outcomes (i.e., several years after exposure). The purpose of this study was to describe one elementary school's RtI implementation process and to examine students' long-term reading comprehension outcomes following their exposure to various phases of implementation. Four cohorts of students who experienced different implementation phases (i.e., a baseline condition or Phases I, II, or III of implementation) during Grade 2 were subsequently followed across Grades 3, 4, and 5 to examine their outcomes on two reading comprehension measures. Results indicated that students who experienced the early phases of RtI implementation (i.e., Phases I and II) during Grade 2 generally had higher mean comprehension scores in Grades 4 and 5 than students in the baseline condition. Implications for practice and future research are discussed.