Recent findings demonstrate that the most effective reading instruction may vary with children's language and literacy skills. These Child x Instruction interactions imply that individualizing instruction would be a potent strategy for improving students' literacy. A cluster-randomized control field trial, conducted in 10 high-moderate poverty schools, examined effects of individualizing literacy instruction. The instruction each first grader received (n = 461 in 47 classrooms, mean age = 6.7 years) during fall, winter, and spring was recorded. Comparing intervention-recommended amounts of instruction with observed amounts revealed that intervention teachers individualized instruction more precisely than did comparison teachers. Importantly, the more precisely the children received recommended amounts of instruction, the stronger was their literacy skill growth. Results provide strong evidence of Child x Instruction interaction effects on literacy outcomes.