In this article, I present a developmental model of how children learn to comprehend what they read, which builds on current models of reading comprehension and integrates findings from instructional research and evidence-based models of development in early and middle childhood. The lattice model holds that children's developing reading comprehension is a function of the interacting, reciprocal, and bootstrapping effects of developing text-specific, linguistic, and social-cognitive processes, which interact with instruction as Child Characteristic x Instruction (C x I) interaction effects. The processes develop over time and in the context of classroom, home, peer, community, and other influences to affect children's development of proficient reading comprehension. First, I describe models of reading comprehension; then, I review the basic processes in the model, the role of instruction, and C x I interactions in the context of the lattice model. Finally, I discuss implications for instruction and research.