Children's Mental Health Service Expansion Act

Sets forth qualifications, including education and licensing requirements. Limits the program to U.S. citizens or permanent legal residents. Grants priority according to financial need, methodology, and willingness to work with high priority populations in the public sector. Treats such grants as equivalent to those of the National Health Service Corps Programs.

Authorizes additional grants for clinical and graduate and paraprofessional training to accredited schools and State-licensed mental health organizations, respectively. Gives priority to applicants with the demonstrated ability to collect data on the numbers trained, certain methodology, and programs to increase the numbers of professionals and paraprofessionals serving high priority populations. Requires training to prioritize cultural competency.

Amends the Social Security Act to increase the number of child and adolescent psychiatry residents permitted to be paid under the Medicare Graduate Medical Education Program. Extends the Medicare Board eligibility period for residents and fellows in child and adolescent psychiatry.

Directs the Administrator to study and report to Congress on the distribution and need of child mental health service professionals.