The ABCD Study is the largest long-term study of brain development and child health in the United States.
Adolescent Brain Cognitive Development
The ABCD ReproNim course provides training for reproducible analyses using the ABCD dataset.
Data/variables can be explored here: https://data-dict.abcdstudy.org/?
Study protocols can be found here: https://abcdstudy.org/scientists/protocols/
And here's an ABCD discussion forum for further questions: https://github.com/now-i-know-my-abcd/docs/discussions