Try the tail feather method.Pullets will have longer tails.At 3 weeks what clues are you looking at to sex? I know I have a 50/50 shot at guessing...I'd like to change those odds! Lol but so far I must await the crow. I've read 3 row combs/boy, 1 row combs/girl, thicker legs, taller stance, darker feathers (i have wheatans), wider combs, sweeter chicks(nice sweeties turning into mama boys then bad boys lol) are indicators of males. Lighter more even feathering/girls, sassy chicks, single comes, squatted stances are female indicators. But nothing has shouted "Yes its a roo" or "Yay! It's a pullet" to me (except my brain screams constantly it wants all girls when I am observing them, its biased lol)