Interested in advice on this too.   We have four new pullets - age 3-4 months and trying to integrate with existing flock of four 7 month old hens.    I have a 6x6 coop and a 6x10 covered run.  Currently we put a chicken wire partition in the coop so the new four have their own "safe" space, and giving the existing girls the end of the coop with access to the run.   We thought a 36" high partition would be sufficient, with up to the ceiling area in the part where the roosting bars are.   Today my husband checked on them all at lunchtime and found 1 of the younger girls in the run being chased by the big girls, and 1 big girl in the coop on the wrong side of the partition.  Ugh. (at present 4 youngsters in the coop, 4 original chickens in the run with the pop door closed.)   There has been some pecking at the young ones through the partition.  At least in the coop they should have enough room to get away from the partition to stay safe from pecking.   I guess when I get home from work tonight we need to add another section of chicken wire to close up the rest of the upper part.    How long does anyone think it will take for them to stop being "too mean" to the little girls?