I found this pic:You can guess based on the wing feathers (shorter, later development- cockerel, longer, feathered out earlier- pullet) but I'm loathe to believe it until more secondary characteristics are more obvious. I still have one black Orpington chick who appears to be undecided. It feathered early, but the comb is suspiciously large and is beginning to get some red. My Australorp cockerel is obviously a boy and just like his dad.
So if I see something like shown they are pullets? Sorry to be such a pest!