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…

The traditional view of development is stage-like progress toward increasing complexity of form. However, the literature cites many examples in which children do worse before they do better. A major challenge for developmental theory, therefore, is to explain both global progress and apparent regression. In this article, we situate U-shaped…