My 7-year-old (almost 8) has ADHD. If it is possible, go into the classroom and observe him. When I did this a couple years ago I saw obvious and striking differences between DD and the other kids. DD was just fine with reading and would stay on task, even in the classroom. But math and writing were different stories. One thing that I need to point out is that people/kids with ADHD ARE capable of focusing on things that highly interest them (sometimes hyperfocusing). So DD, for instance can put together a 100 pc. jigsaw puzzle in one sitting or read 3 chapter books in a row even when she's not on her meds. She can get obsessed with ThinkFun puzzles and complete puzzles that most adults would give up on after a minute. But if you ask her to do something that is not completely engaging to her she falls apart, even if she WANTS to do a good job. In this way it can be hard to differentiate between a gifted kid who is simply bored, and a 2e gifted kid with ADHD.
In the classroom (when not on meds), DD is highly distractible with written work and spends most of her time looking around the room at other kids. She is incredibly SLOW and her processing speed seems off. She will get "lost" in the hallway, chatting with people rather than going to wherever she is supposed to be going. If your DS is on task most of the time and can get work done at the same speed as the other kids (assuming he is trying), he probably doesn't have ADHD.
You may also want to ask about Developmental Coordination Disorder. Fine motor skills like writing can be affected even if there is no dysgraphia.
