I'm an advocate of every child getting instruction at their level and pace and having opportunities to learn and socialize with intellectual peers. Ideally, everyone should have a decent shot at being the top student in most of their coursework if - and only if - they work hard to master material that is cognitively challenging to them.
The further out from the mean of functioning you are, the harder it is going to be to find academic peers who are also age peers and emotional peers, and the more likely it is that this difficulty in finding people you can identify with who get your jokes and understand your questions and feelings will have social and emotional consequences. I don't think there is a hard IQ percentile cutoff for having the kinds of needs that we associate with the gifted. I think there is a gradient, and whether someone near the left hand side of the range will seem and feel different and need differentiated instruction really depends on the environment in which they find themselves.
