by 6 weeks if you can post pics most of us can give you an accurate guess on gender...we all tend to look at (give or take depending on breed) their coloration, the size and color of the comb and wattles, and the leg size. now if you have silkies those you will tend to have to wait till they crow or lay, there are other breeds that tend to be hard to sex as chicks to....also if you have sex links those can be told apart at hatch as males and females are different colors, with barred rocks and doms those can also be sexed as chicks with their fuzz by the head spot and the color of the legs (no this isnt always accurate though)
what breeds do you have?