I did this with my straight run buff orpingtons last year and it was correct for all 4 (1 roo, 3 hens). I tried to do it with my easter eggers this year, I got 3 and all had the double row but at 8 weeks old I am still questioning whether 2 of the 3 are pullets or cockerels, 1 I am pretty sure is a pullet
The pictures are my last years chicks, top was in fact a roo (I marked his head with a blue marker after I feather sexed them) and bottom was a pullet
The pictures are my last years chicks, top was in fact a roo (I marked his head with a blue marker after I feather sexed them) and bottom was a pullet