Some dynamic systems approaches posit discontinuous changes, even universal stages, in development. Conversely, Thelen and colleagues see development as gradual because it relies on real-time interactions among many components. Yet their new model hinges on one parameter, neural cooperativity, that should change discontinuously because it engenders new skills that catalyze neural connectivity. In fact, research on cortical connectivity finds development to be discontinuous, and possibly stage-like, based on experience-dependent and experience-independent factors.