Decades of research have documented in school-aged children a persistent difficulty apprehending an overarching biological concept that encompasses animate entities such as humans and nonhuman animals, as well as plants. This has led many researchers to conclude that young children have yet to integrate plants and animate entities into a concept…

As the articles in this issue attest, U-shaped curves in development have stimulated a wide spectrum of research across disparate task domains and age groups and have provoked a variety of ideas about their origins and theoretical significance. In the authors' view, the ubiquity of the general pattern suggests that U-shaped curves can arise from…