Is someone with inattentive adhd much less likely to be diagnosed with the disorder by the age of 7 as compared to the classic hyperactive adhd child?

I am an adult : Psychiatrist and i don't meet too many hyperactive adhd folks who were missed in childhood but I do end up diagnosing some with add. It is certainly less obvious.

Yes it is harder to: Diagnosing add usually takes longer than adhd. You cannot miss the hyperactive child with attention deficit. They can't sit still and get in trouble in school pretty quickly when they are expected to sit and listen. When a child just has add their symptoms are more subtle. They are often seen as lazy since they have difficulty completing tasks and are diagnosed later or not diagnosed but failing.

Yes: Children with the inattentive form of ADD may be thought of as disinterested, board, not trying hard. If there is any question of inattentiveness, a thorough evaluation should be done and an Individual Educational Plan IEP should be developed to help in school.