In this application we propose to examine the efficacy of a specific movement-based mindfulness intervention for children with ADHD - Tai Chi. This approach was chosen for a number of reasons: 1) extensive documentation in the research literature, 2) engagement afforded by a martial approach to mindful movement, and 3) scalability given the existing availability of Tai Chi instruction in the United States and the ease of performing gentle Tai Chi movements even in the presence of physical limitation. Consistent with the "Fast-Fail" approach in the first two years (R21 phase) we will investigate the impact of Tai Chi on the motor system targets our lab has established as highly correlated with measures of classic ADHD symptoms. Specifically, we will measure SICI (short-interval intra-cortical inhibition via TMS) and overt movement behavior resulting from failures of motor control (mirror overflow and motor impersistence). Milestones will comprise successful motor system target engagement in the context of Tai Chi training. The findings will lay a foundation for the clinical exploration of Tai Chi and other movement-based mindfulness training approaches in ADHD and other conditions where the motor system is implicated. Our brain-based approach further provides a clear path for reliable assessment as well as integration with the cognitive neuroscience literature on inhibition and other aspects of cognitive control.