Don't be too hard on the teacher, not until you've had a chance to sit down and listen, and then talk. The teacher knows this is a bright kid and is frustrated at the apparent lack of consistency in his results. And from the teacher's point of view, she has seen other cases where a kid suddenly drops below their standard for reasons which can be improved with intervention of some sort.
Whatever you are privately thinking about the teacher, go in there (meet with the teacher) with an air of "Let us work together to help this child."
Something is not working, and fairly recently. The teacher in this case seems to have been the first one to notice, perhaps because this is a problems first showing up in school rather than at home.
It could be a false alarm, or it could be a change in direction of your son's ADHD. A good teacher will report a concern so you can then communicate back, and also if you feel you need to, with the specialist.
Far better to have an early (maybe false) warning, than to not be told of problems until the yearly report comes in.
Talk to the teacher, if after you meet you feel the pressure is too great then discuss with the teacher some options to reduce the workload in areas your son is struggling, and perhaps determine where he is having difficulty and where he is still achieving at a high level. Then see if you can use the high abilities to resolve the learning problems possibly beginning to emerge.
We've been through this with our kids. With easy child 2/difficult child 2, initially she was deliberately dumbing down in school because she hated being called a nerd. On the one hand she was doing the work for other kids to help them get through, but neglecting her own or deliberately getting it wrong, in order to be more popular. We finally said to her, "You are a bright kid. When you do worse than your best, you will not feel so good about yourself. That is not healthy for you. It is also a bad habit to get into. Also, when you do other kids' work for them, the teacher doesn't get to know where they need help. The teacher may push them further ahead than they are really ready, and their learning will suffer later on. It's always best to be honest. And because you're a smart kid, you will always have friends, and always have enemies. Like everybody. Better to have people feel the way they do about you because of who you really are, than because of who they think you really are."
We also told her that a true friend would love her for who she is, and would not want her to choose to do badly, to make them feel better. Someone who wants her to do badly is NOT a true friend, it is someone who is jealous and knows they can't work to her standard; they want her to do badly to give them a better chance, but winning under those conditions is not a win and it is not right.
She had to choose - be popular, maybe; or do well. And in 20 years time, a choice to do well would still be seeing her right. A choice to be popular would see her still needing to make new friends as her circle of contacts would always be changing through life. Now she is 24, she has lost contact with any of those who she was friends with in elementary school. She has a lot of friends, she is happy in their company, and they rejoice when she achieves. She made a good choice.
But part of her problem also, was hitting the wall academically and socially despite brilliant beginnings. Watch for this - we didn't believe it at first either. I wish we had.
Marg