This randomized control study compares the efficacy of two response-to-intervention (RTI) models: (1) Dynamic RTI, which immediately refers grade 1 students with the weakest skills to the most intensive intervention supports (Tier 2 or Tier 3); and (2) Typical RTI, which starts all students in Tier 1 and after 8 weeks, decides whether students who did not respond to general instruction in Tier 1 should move to Tier 2. The study asks: (1) What are the effects of Dynamic RTI and Typical RTI on student reading outcomes by the end of first grade?; and (2) Does assignment to specific tiers predict gains on standardized assessments, and does this differ when comparing Dynamic and Typical RTI groups? The setting is seven schools in a school district in a mid-size city in the southeast in their first year of RTI implementation. Approximately 500 students participated in the study; less than 3% were Limited English Proficient, and student socioeconomic status varied across schools. Matched pairs of students within classrooms were assigned to either Dynamic or Typical RTI. The only difference between conditions was "when" students were provided supplemental intervention sessions. Reading assessments included letter-sound, word, passage reading, and teacher-reported severity of reading difficulties. Results of the analysis revealed that: (1) Students in the Dynamic RTI group had statistically significantly higher Spring Reading scores than did students in Typical RTI, with an effect size of 0.36; (2) Tier 2 students in the Dynamic RTI condition had significantly higher reading outcomes scores compared to students initially eligible for Tier 2 in Typical RTI; and (3) Students initially eligible for Tier 3 had the weakest scores over the school year, but students initially eligible for Tier 3 who received the Tier 3 intervention immediately because they were in Dynamic RTI achieved higher Brief Reading scores compared to Tier 3 students in Typical RTI who had to wait until the beginning of Session 3. Dynamic RTI protocols, such as the one used in this study, suggest that there is no reason to delay intervention; that any effect of false negatives is negligible; and that, broadly implemented, Dynamic RTI, including a foundation of effective Tier 1 instruction, can improve reading outcomes for all children. The study was conducted for a full school year, and was unique relative to prior RTI investigations in allowing movement across tiers every 8 weeks in tandem with report card periods and in allowing fast tracking to Tier 3 for the most needy students. Table and figures are appended.