A fundamental question in psycholinguistics concerns how grammatical structure contributes to real-time sentence parsing and understanding. While many argue that grammatical structure is only loosely related to on-line parsing, others hold the view that the two are tightly linked. Here, I use the incremental growth of grammatical structure in developmental time to demonstrate that as new grammatical knowledge becomes available to children, they use that knowledge in their incremental parsing decisions. Given the tight link between the acquisition of new knowledge and the use of that knowledge in recognizing sentence structure, I argue in favor of a tight link between grammatical structure and parsing mechanics.