It is hard to explain I can just tell with some of them. Been raising them about 12 years now and it is one of those things you can just tell but you can't explain how. It has to do with the body shape, the attitude, how the hold themselves I can't really explain it.

In China they actually teach people to sex chicks this way. They use a scanner to test chicks and let the person say boy or girl. It takes about 6 months and even though there is no difference after that time they are 98% accurate. They are just told correct or incorrect and in time what ever there is to show it, they see when others don't.

Note - That factoid popped up on an early 00s series called White Collar and I tracked it down with some effort and it vetted true.