Does music help a child's development and health? A positive impact of music is supported by a rapidly growing body of scientific work that has shown that musicians' brains are shaped by music in ways that could underlie benefits of musical training not only on musical abilities, but also on fundamental non-musical skills such as attention, executive function, social/emotional functioning, and language, skills that form the foundation for healthy functioning academically and in society. Despite this, deep questions remain: does music participation cause change, or is it a reflection of some underlying, general factor? What is the relative contribution of music activity vs. music ability? To complement past studies (which have typically relied on correlative observations along with some small-scale intervention trials and longitudinal studies) there is now an unprecedented opportunity to leverage large-scale, high-dimensional neurodevelopmental studies by creatively nesting within them questions about the impact of music and development, focusing on active participation in music training. Such an approach is attractive in its power and resource efficiency. This three- year project seeks to address the impact of music training on development using two approaches building on our prior work: 1) Detailed analysis of existing large-scale longitudinal neurobehavioral data from the PLING/SIMPHONY study, and 2) Analysis of initial data and laying of further groundwork to empower the unprecedented ABCD (Adolescent Brain and Cognitive Development) study of over 11,000 youths over 10 years, to comprehensively address the role of music in brain and cognitive development and physical and mental health. Together, these two resources span the school years, collecting thousands of behavioral and brain variables for each individual and timepoint. This proposal will apply new methods in development to build models of the impact of experiences on the development of brain and behavior with an unprecedented detail.