ADHD is not a form of learning disability in special education terms, although many students with ADHD also have learning disabilities. Students with ADHD whose disability restricts one or more major life activities can receive a program of instructional services to meet their needs using something called a 504 Plan. This means that you can meet with his teachers and the school psychologist to discuss what types of accommodations would help your son learn in the classroom.
Here are questions and answers about ADHD and special services from lawyer Matt Cohen.
And here is information about ADHD and the law from special education lawyer Peter Wright's website, Wrightslaw.
Since this information often gets complicated, it's a good idea to look it over with someone else so that you can approach the school with a clear sense of your rights under the law and have an informed discussion about getting your child the right accommodations so that he can learn in school.
You can also seek support from your local CHADD chapter, which specializes in ADHD issues. Here is a link to the chapter locator. The CHADD site also contains information about support groups and managing ADHD at school and at home.