I was a special ed teacher for a year and our district does not allow kids with ADHD as their only exceptionality into special ed. ADHD is Other Health Impaired and they have to be gifted or LD or something else to get in. In fact, my nephew had a placement meeting and his IQ was a little too low so he ended up not in special ed and his ADHD didn't get addressed.
I have been thinking about getting him on a 504 to help address a few of the issues at school that boil over into the home life. Just to answer the original question, 504's provide modifications for kids that have health issues that effect their school work. He has to read thirty minutes every night and it is really tough to fit it in with the long list of homework and his bedtime routine since his meds wear off soon after he gets home. I would like for him to be able to read less during the week and more on weekends. And, he always forgets something at school, be it his planner, his lunch box, one of his books, his jacket. He is smart and should be held to high standards, especially when he is on his meds, but there are some things he just can't get to.
Is our school district misapplying the law? I guess I could research it myself...but it wouldn't be aby fun to sue the school district to get him in. We are probably putting him into a private school next year anyway.