My yard is a Chicken Compound, with multiple coop buildings. I have "grow-out" coops for the youngsters, with their own penned areas within the main area. They get their own feeder & waterer, stay there for two weeks (after they're around 8 weeks old or so) and then I just pull up the temporary fence made from garden stakes and chicken wire. They will have had two weeks "beak to beak" as someone already mentioned, hearing each other, seeing each other, and thus becoming known to the flock. When the newbies are released, they are no longer strangers. There's some pecking order issues, but very minor ones.
I kinda went all out on the grow out coops thing, but you can do the same with a plastic dog house, plastic Little Tikes playhouse, etc. Just a place for them to sleep at night, with a bit of temporarily fenced space for a small "run," until they are large enough to join the main flock.