My DH, an ex-commercial chicken farmer, is sitting behind me and he's awful chatty tonight. I read your question outloud to him and he said to "look under their tail". I've 
him for you. 
With sex linked chicks, you can tell by the color at hatch. Easy, except you're not dealing with sex links. With breeds bred to be wing-sexed, you can tell by checking the growth pattern of the wing feathers. You're not dealing with chicks bred to be feather-sexed.
That leaves two options. Watch for the secondary sex characteristics to develop between 4 to 6 weeks or wait for a crow or an egg.
With a batch of chicks from the same parents, or breeds of parents, the secondary sex char. should be semi-easy. Here's what to look for:
According to UC Davis Veterinary Care Program.
2. Physical Characteristics (4-6 weeks of age)
a. Comb The cockerels comb is medium size and pinkish, the pullets is small and yellowish.
b. Legs The cockerels legs are sturdy and long, the pullets are finer and shorter.
c. Tail The cockerels tail is stumpy and curved, the pullets is longer and straight.
d. Back The cockerel has a thin line of stub feathers down the center of his back, the pullet has more advanced feathering along the center of her back.
e. Side of neck, flank and crop The feathering in the cockerel in these areas is poorly advanced, the pullets feathering in these areas is well advanced.
f. Wing bows In the cockerel the wing bows are bare, in pullets the wing bows are covered with small feathers.
Good luck with your hatch! 
