A longstanding and fundamental debate in developmental science is whether knowledge is acquired through domain-specific or domain-general mechanisms. To date, there exists no tool to determine whether experimental data support one theoretical approach or the other. In this article, we argue that the U- and N-shaped curves found in a number of studies across a range of developmental areas are a product of domain-general learning. This pattern arises through a combination of improving cognitive capacities, which allow for different levels of processing, and emergent constraints on learning. We propose that developmental scientists' knowledge of the meaning of this pattern can aid the theoretical interpretation of data as well as experimental design to incorporate a sufficiently inclusive range of ages. (Contains 1 figure.)