Who do you think is the best boy in our class?
I think this structure is not grammatical. I think the correct one should be:Who do you think the best boy in our class is?
Because we say "Do you know who the best boy in our class is? instead of"Do you know who is the best boy in our class".
Am I correct?
Both word orders are commonly used by fluent English speakers. If there's some textbook rule that says one or the other is wrong, it just leads us to that perennial argument we have on this site about whether "correct language" is what is written in some authoritative book, or what a sufficient number of sufficiently educated people actually say and write.
But in this case, if there is a rule, I think it's a pretty obscure one. So I'd simply say, either is correct.
