Children's engagement is an important construct often reported in early intervention and early childhood special education. However, its utility depends on its definition, measurement, theory of change, and empirical evidence. Our purpose is to discuss innovations in children's literacy engagement (CLE) and report empirical evidence demonstrating how these advancements can be used to promote children's learning and school readiness. We discuss five specific innovations: (1) defining CLE as the behavioral target of intentional instruction, (2) directly assessing CLE using the CIRCLE ecobehavioral observation system, (3) including CLE in a larger framework of instructional decision-making, (4) evaluating new CLE-focused instructional interventions, and (5) supporting children who are not responding to instructional intervention. We describe how these innovations help address the questions of "under what conditions" and "for whom" preschool instructional interventions are effective. Implications are discussed.