Bringing effective, research-based literacy interventions into the classroom is challenging, especially given the cultural and linguistic diversity of today's classrooms. We examined the promise of Assessment-to-Instruction (A2i) technology redesigned to be used at scale to support teachers' implementation of the individualized student instruction (ISI) intervention from kindergarten through third grade. In seven randomized controlled trials, A2i and ISI have demonstrated efficacy. However, the research version of A2i was not scalable. In order to bring A2i to scale in schools serving linguistically diverse students, we carried out the current study across two phases. This study represents both an exploration of what it takes to bring an educational intervention to scale (Phase 1) and a quasi-experiment on the literacy outcomes of learners whose teachers used the technology (Phase 2). We integrated assessments of vocabulary, word decoding, and reading comprehension; revised the A2i algorithms to account for the constellation of skills English learners (ELs) bring to the classroom; updated the user interfaces and added new graphic features; and improved bandwidth and stability of the technology. Findings were mixed, including several non-significant results, a marginally significant intent-to-treat effect on word reading in kindergarten and first grade for English monolingual students and ELs, and one significant interaction effect, which suggested ELs and students with less developed reading skills in second and third grade benefitted most from the intervention. With some caution, we conclude that A2i demonstrates potential to be used at scale and promise of effectiveness for improving code-focused skills for diverse learners.