usually the cockerels will be the first ones to start to show pinkish wattles start to hang down under their chin. Their comb stands up a little higher and gets pink quicker than the girls. Then they start to get their pointy hackle (neck) and saddle (on their back, in front of their tail) and if they are copper or birchen or some other color combo they will be bright different colors. When they are younger, sometimes you can tell by looking at their feet. Their joints just below the feathers are usually thicker and the shank bone between that joint and the feet is thicker and heavier built than in the baby girls. When you see them walking around, even as young as a week old, the most dominant cockerel will have more upright posture, often his head and neck will be a third higher than the other chicks. Hope some of that helps... None of these rules is hard and fast, or stand-alone. It is just the preponderance of evidence when you compare all these traits. Good luck!