Newbie with straight run Barred Rock chicks (6)...

[Ol Grey Mare]

You can usually see the difference in barring by about 4 to 6 weeks with purebred Barred Rocks.

Males have two copies of the barring gene. Females can only have one copy. This means that males have twice as much white as females. Males have wider bars of white, and more narrow black bars.

X 2 - the differences are generally fairly easy to spot well before 10 weeks, as these little ones start to feather in you'll get a good idea of what you ended up with.