The chapter discusses the study of brain-behavior relationships during development, focusing on the dorsolateral prefrontal cortex (DLPFC) and its role in cognitive abilities. The author, Adele Diamond, suggests guidelines for conducting and evaluating such research, emphasizing the importance of convergent and divergent validity. Convergent validity involves using multiple tasks linked to the same neural circuit to ensure that improvements or impairments are not due to diverse causes. Divergent validity requires demonstrating that other neural regions are not responsible for the observed performance on these tasks. The chapter also highlights the importance of studying the effects of damage to mature and developing systems differently, as well as the need for direct evidence from children in addition to animal studies. The author uses the delayed response task, object retrieval task, and A/B task to illustrate these guidelines, showing that DLPFC is crucial for memory and inhibitory control. The chapter concludes by discussing the remaining questions about the development of DLPFC and the abilities it supports after 12 months of age.The chapter discusses the study of brain-behavior relationships during development, focusing on the dorsolateral prefrontal cortex (DLPFC) and its role in cognitive abilities. The author, Adele Diamond, suggests guidelines for conducting and evaluating such research, emphasizing the importance of convergent and divergent validity. Convergent validity involves using multiple tasks linked to the same neural circuit to ensure that improvements or impairments are not due to diverse causes. Divergent validity requires demonstrating that other neural regions are not responsible for the observed performance on these tasks. The chapter also highlights the importance of studying the effects of damage to mature and developing systems differently, as well as the need for direct evidence from children in addition to animal studies. The author uses the delayed response task, object retrieval task, and A/B task to illustrate these guidelines, showing that DLPFC is crucial for memory and inhibitory control. The chapter concludes by discussing the remaining questions about the development of DLPFC and the abilities it supports after 12 months of age.