This randomized controlled trial in 55 low-performing schools across Florida compared 2 early literacy interventions--1 using stand-alone materials and 1 using materials embedded in the existing core reading/language arts program. A total of 3,447 students who were below the 30th percentile in vocabulary and reading-related skills participated in the study. Both interventions were implemented with fidelity for 45 minutes daily for 27 weeks in small groups of 4 students (or 5 in grade 2). The standalone intervention significantly improved grade 2 spelling outcomes relative to the embedded intervention; there were some differential impacts due to cohort and baseline and, in kindergarten, to English-learner status. On average, students in schools in both interventions showed similar improvement in reading and language outcomes and similar percentile gains to those in recent systematic reviews. Results are discussed with respect to alignment of Tier 2 instruction with Tier 1 instruction. [This paper was published in "Elementary School Journal" (EJ1171896).]