FACTS - A Section 504 committee will review EXISTING data to determine if an impairment is creating a substantial limitation to a major life function. This is NOT a formal evaluation with testing, and a committee does NOT diagnose a student with an impairment(s).
When it pertains to ADHD, the committee cannot require a doctor's diagnosis. The US Department of Education provides specific guidance about the rights of students with ADHD. A medical diagnosis can be considered but not required. If the team has collected enough data to determine that 'characteristics of ADHD' are creating a barrier to the student's learning, the committee can review the data and determine if the 'characteristics of ADHD' are substantial enough to meet the definition of a disability.
With or without a medical diagnosis, there is NEVER automatic eligibility for Section 504. Eligibility is always determined by a committee based on the data and on a case-by-case basis.
For more information on eligibility, refer to the Dept. of Ed FAQs on evaluation