Good to know! Haha. My husband was quite convinced that it would be accurate based on what they do in large chicken operations where they get rid of the roosters on day 1. But obviously those are bred with that trait purposefully and most of mine are just a backyard mix.
Yes, it can be quite accurate when they are bred to have the right genes. But it's unlikely to work with yours.
So I guess I will not know for awhile which ones are actually pullets vs. cockerels. When can you usually tell? I really hope I don't have a bunch of roosters to get rid of
Some males become obvious as young as 3-4 weeks old, because their combs & wattles get much larger and redder as compared with the females.
Many males are obvious by about 8 weeks old, because their combs & wattles are bigger and redder. Some start crowing by this age.
The males eventually get male-specific saddle feathers (narrow with pointy ends, that eventually grow long and hang down on each side of the tail.) Those often start growing around 12 weeks of age, although some people are good at recognizing them as tiny little feathers while others don't notice until the feathers have grown quite long.
Some late-maturing males keep folks guessing until 6 months or more, because they continue to have a small/pale comb, don't grow the saddle feathers until late, and do not start crowing. Males that stay incognito for that long are fairly rare, but they definitely exist.
You can be sure of having a female when she lays an egg. When some chickens have started to lay, you can go examine the vents of them all (the hole that poop & eggs come out of), and see who is laying. The vent will look bigger, more moist, and able to stretch if the bird is laying eggs. It will be smaller and look more dry and puckered up for any chicken that is not laying (chicks, roosters, broody hens, molting hens.) If you look at some that are laying and some that are not, the difference is usually pretty obvious.
Crowing at any age indicates that the bird is probably male. (Hens that crow are fairly rare, although they do exist.)
Some chicken breeds have males and females with different coloring, but I would not count on that with barnyard mixes.
Of course some of those things appear much sooner than others. It's common to have the genders all identified by 8-12 weeks old, although of course there are some that are clear earlier or that keep you guessing for several more months.