This randomized control trial examined the efficacy of a multitiered supplemental tutoring program within a first-grade responsiveness-to-intervention prevention model. Struggling first-grade readers (n = 649) were screened and progress monitored at the start of the school year. Those identified as unresponsive to general education Tier 1 (n = 212) were randomly assigned to receive Tier 2 small-group supplemental tutoring (n = 134) or to continue in Tier 1 (n = 78). Progress-monitoring data were used to identify nonresponders to Tier 2 (n = 45), who were then randomly assigned to more Tier 2 tutoring (n = 21) or one-on-one Tier 3 tutoring (n = 24). Tutoring in Tier 3 was the same as in Tier 2 except for the delivery format and frequency of instruction. Results from a latent change analysis indicated nonresponders to Tier 1 who received supplemental tutoring made significantly higher word reading gains compared with controls who received reading instruction only in Tier 1 (effect size = 0.19). However, no differences were detected between nonresponders to Tier 2 who were assigned to Tier 3 versus more Tier 2. This suggests more frequent 1:1 delivery of a Tier 2 standard tutoring program may be insufficient for intensifying intervention at Tier 3. Although supplemental tutoring was effective in bolstering reading performance of Tier 1 nonresponders, only 40% of all Tier 2 students and 53% of Tier 2 responders were reading in the normal range by grade 3. Results challenge the preventive intent of short-term, standard protocol, multitiered supplemental tutoring models. (Contains 2 figures and 7 tables.)