I also want to add, for further clarity, that even though children look different at home vs at school, children who have ADHD, prior to their entry to school, have a typical profile that parents can easily identify. They have a history at a very young age, of restless frequent movement, poor attention and focus to parental requests, inability to do one task for very long, unless highly interested in the task as it is very common for children with ADHD to hyper focus on what interests them.
You are right, contact maya, to question why you didn't see evidence of ADHD as a very young child. This is exactly the reason to dig deeper to look for learning problems that are creating the "look" of inattention or lack of focus in school. While I relate to your situation, in the sense that I was also told (falsely) that my son had ADHD by teachers, and I intuited something more was going on, I think you will meet or talk to people who have the opposite situation and wish that they had accepted a diagnosis sooner such as some of the responses above.
I think it's important to listen more to your own voice though, as I believe most mothers have an intuition that they need to follow about how to help their child. Listen to it. I only hope to validate you own voice. I also used to think, "if only it were as easy as taking a pill"....not that I shrug off side effects or would minimize the work involved in helping a child with ADHD. I just KNEW though that something more complicated was going on for my son and wished I could just accept the more "obvious" answer.
OK....I hope you let us know how things go. If your school gives you any difficulty regarding testing, please come back on the board with a different thread about it. I know many parents here can give great advice about your rights.