The central question of this book, "how to decide when, or if, people of certain ages are 'able' to do certain things," prompts consideration of a more general question-" how to characterize growth or developmental change ." Certainly many useful data-analytic methods are available to address these fundamental questions . Here, we discuss the fitting and testing of convergence hypotheses using latent growth curve structural models (LGM). We find these methods both powerful and under utilized in the identification and understanding of changes in behavior over time. By fitting these models to data on changes in antisocial behavior during adolescence, we illustrate the potential utility of these methods for structuring questions related to the development of competencies . Throughout this discussion we hope to emphasize the compatibility of these methods with current concerns for establishing "criteria for competence ." In particular, we emphasize the utility of these methods in formalizing a variety of testable hypotheses that may be of interest to developmental psychologists whose research addresses questions of competency.