I tried it with my last hatch of 7 and it was reasonably accurate. At one week of age the pullets appear to be more feathered than their brothers. The tails start earlier on the girls and the wings are more feathered. Out of my 7, 3 appeared to be pullets and I banded them with a pink cable tie. Now at 4 weeks, the "girls" seem to be 2 pullets and 1 cockerel. So I have 5 cockerels and 2 pullets. Gotta take that sissy pink band off the cockerel!