The articles featured in this issue make apparent the variety of perceptual and cognitive competencies that follow curvilinear developmental courses as well as the complexities inherent in accounting for such phenomena. What is revealed is the way in which a fit is achieved between organisms and the environments they occupy. Curvilinear…

When a behavior disappears and then resurfaces, developmental psychologists typically look more closely at the behavior to figure out what is different before and after--that is, they increase the grain with an eye toward discovering how the system that generates that behavior has changed. But what ought to count as a U-shaped phenomenon? How…

The articles in this collection consider one very interesting puzzle of development: U-shaped developmental functions. At some point during development, an organism might exhibit what seems like a regression from its expected developmental trajectory and, according to continuity models of development, this is aberrant. In this special issue,…