I should have stated, "some" of the gifted students at my school have difficulty relating to age-level peers.
How many of their age-level peers have difficulty relating to the gifted students? Children aren't always kind to those that stick out. Some gifted children may be inclined to overcome that barrier, while others aren't. Teachers should spend at least as much time trying to get normal children to remove that barrier as they spend asking the gifted children to do the same.
When I was in school I found my friends to be others who didn't fit the mold for whatever reason. Sticking out brought us together. When I went to a top university, that all changed. Being smart didn't set me apart from my peers because we were all smart. I made friends with anyone and everyone. Now I work exclusively with engineers, and again, I am friends with anyone and everyone. This is not due to some elitist perspective on my part. Many of my best friends are of less than average intelligence (much to my mother's puzzlement.)
All of the children should be expected to accept different children.