My son was diagnosed in 1st grade and he did not want to take the medicine. I had some very good mentors who were kind and sweet and I read some great books (The gift of ADHD and some others about different learning styles such as The Way They Learn, etc.)
My son and I always read books at bedtime (along with his older sister) and I used that quiet time together to explain to him how everyone's mind works differenty and that his mind is usually moving faster than his hands and mouth can move. Nothing bad about ADHD, but that medicine would help him pay attention in class. He wanted to do that becusae he didn't like being singled out. I reminded him of different people we know who take medication for different things (dad for cholesterol, etc.) and that helped a lot.
Be prepared that he'll go through times in his life where he won't want to take the medicine. We had a period of time in 3rd grade and again in 5th. Sometimes it was becuase he was certain that it made him different and no one else in his class was taking medicine. I assured him, as did his teacher, that there were more than a couple of kids who took medicine for different reasons. I think he wanted to exert some control over his life and I understood that. He also didn't like how one of the medications made him feel so the doctor tried something different which was a better fit. He actually stopped taking it for a few months in 3rd grade and it was a tough time for him in school - and he realized it after it was done.
He's now in 7th grade and doing well. He still takes the medication, and although he's much bigger than he once was his dosage is only a tiny bit higher - he doesn't need that much and probably didn't need even the lowest dose when he was only 6. Some people are more sensitive to medication than others.
Also - keep in mind that ADHA often goes hand-in-hand with minor learning diificulties. My son has language based learning disabilities and had a huge struggle learning how to sound out words, he needed speech therapy and still hates to write anything! But I petitioned the school for testing and special ed and he got it. it was greatly needed. But now at 12, almost 13 he's at grade level and doing really well. He'll never be an author - but he's very bright and may end up being an engineer or builder.
Help your son find the things he's good at and that he likes to do and he'll just blossom before your eyes. My "baby" is now taller than I am - he's 5'10" and will still come in the kitchen and give me a huge hug and a kiss. Love those boys!