I have a beast of a Japanese Bantam, she literally is the size of a Robin, and she attack's the full size hens all the time. I actually was putting her in time out everyday for a week. She went to bed with everyone since that wasn't the problem, and in the morning, she was stuck in the grow out baby run all by herself. I did this for a whole week. Little stinker would still try to get them through the wire, but after about 5 days, she actually looked sad to be in there all by herself all day long. Now she is fine, every once in a while she is a beast, and I throw her in time out. Usually fixes her right up. Good luck.