How to best characterize cognitive development? The claim put forward in this article is that development is the improvement of a kind of coordination among a variety of factors. To determine the development of coordination in a cognitive task, children between 4 and 12 years of age and adults participated in a time estimation task: They had to press a button every time they thought a short time interval had passed. The resulting data series of estimated time intervals was then subjected to a set of fractal analyses to quantify coordination in terms of its degree of "rigidity" (very highly integrated) vs. "looseness" (poorly integrated). Results show a developmental trajectory toward pink-noise patterns, suggesting that cognitive development progresses from a very loose, poorly integrated coordination of factors toward a pattern that expresses more integration, perhaps due to an optimization of constraints, that allows for a more stable coordination.