The elusive "Developmental Mechanism": What they are and how to study and test them

Few issues have garnered as much attention as that of understanding mechanisms of developmental change. Understanding mechanisms of developmental change is important because it allows researchers to go beyond studying at what age an ability emerges to understanding the processes by which those abilities develop in the first place. Despite the clear importance of mechanisms, the notion of a developmental mechanism or mechanism of developmental change remains largely undefined and there exists no clear guidance on how to study these mechanisms systematically in the developmental literature. Given these outstanding questions, this paper has two main aims. The first aim was to provide a clear definition for mechanism and a discussion about what is meant by development. I argue that the definition of mechanism that is provided better aligns with how most, if not all, developmental scientists think about them. The second goal was to provide concrete suggestions for how developmental scientists might study and test different kinds of mechanisms of developmental change. One of the main arguments of the paper is that there is no one-size-fits-all approach to studying and testing mechanisms of developmental change and that how developmental researchers study them depends on key features of the mechanism in question.