Here are just a few resources and studies:

Studies show that a complex physical activity, like martial arts, strengthens neural networks in the brain, and enables kids with ADHD to practice self-control. From ADDitude Magazine: https://www.additudemag.com/kids-karate-adhd-focus-exercise/

The children who attended martial arts classes most frequently exhibited the greatest changes in observed behaviors and those who attended the fewest classes showed the least amount of change. Empirical study of tae kwon do and ADHD from Seton Hill University: https://www.ship.edu/globalassets/proteus/volume25.2-37-cooper.pdf

Children taking part in taekwondo training through a school program showed greater self-regulation, greater social responsibility, and less hyperactivity than those who didn’t: https://www.sciencedirect.com/science/article/abs/pii/S0193397304000309?via%3Dihub

And it’s not just kids! In older adults, taekwondo has been shown to help reverse age-related mental decline.

Age-adapted Taekwondo training improves various aspects of cognitive function in people over 40. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3822408/