This article presents findings of an efficacy trial examining the effect of a multitiered instruction and intervention model on first grade at-risk students' reading outcomes. Schools (N = 16) were randomly assigned to the treatment or control condition. In the fall of Grade 1, students were assigned to an instructional tier on the basis of "Stanford Achievement Test--10th Edition" scores (31st percentile and above = Tier 1; from the 10th to the 30th percentile = Tier 2). In both conditions, students identified as at risk (i.e., Tier 2; n = 267) received 90 min of whole group instruction (Tier 1) and an additional 30 min of daily small group intervention (Tier 2). In the treatment condition, teachers were trained to enhance core reading instruction by making instruction more explicit and increasing practice opportunities for students in Tier 1. In addition, at-risk readers were provided an additional 30-min daily small group intervention with content that was highly aligned with the Tier 1 core reading program. Results indicate significant, positive effects of the intervention on students' decoding and first semester fluent reading and potentially positive effects on reading comprehension and total reading achievement.