Tail feathers a good indicator of sex?

[MotherOfMany]

We have 7 chicks that are about 5 weeks today. One we are CERTAIN he's a roo. The others we are still waiting. Our roo's tail is stubby, lays flat (horizontally), and has a slight curve down towards his feet. Five of my other chicks tails stand very upright and come together making a vertical line tip. I have one other chick that's beginning to show signs of flat tail like the roo. Does this mean it's a roo too?

 

[RAWR]

not always
what do their combs look like?

 

[Backyard Hencam]

This guide may help you. It did me. Your chicks are a good age to apply it.

According to UC Davis Veterinary Care Program.
2. Physical Characteristics (4-6 weeks of age)
a. Comb – The cockerels comb is medium size and pinkish, the pullets is small and yellowish.
b. Legs – The cockerel’s legs are sturdy and long, the pullets are finer and shorter.
c. Tail – The cockerel’s tail is stumpy and curved, the pullets is longer and straight.
d. Back – The cockerel has a thin line of stub feathers down the center of his back, the pullet has more advanced feathering along the center of her back.
e. Side of neck, flank and crop – The feathering in the cockerel in these areas is poorly advanced, the pullets feathering in these areas is well advanced.
f. Wing bows – In the cockerel the wing bows are bare, in pullets the wing bows are covered with small feathers.

Good luck!​

 

[MotherOfMany]

All of their combs are different. Ranging from small to large also ranging in color from yellow to peachy.