If I remember correctly, your DS was very good in the past with verbalizing to you when something wasn't working. I think it's important to take him seriously both when he's telling you something's wrong and also when he tells you something's fine. If it were me and it were a low risk situation I would trust his gut over mine. If he decides he was wrong, you can take him out later.

DS6 doesn't do any academic classes through our co-op. One of the leaders was very specific that she doesn't believe that GT kids exist (she's a former public school teacher). There are plenty of non-academic classes offered for him to get the fun, class experience without the stress of yet again being told that there's something wrong with him.