Wing feather sexing only works if the birds are bred for it. It is not instant and reliable on all breeds.
Speckledhen offers good advice on the barred rocks. Sorry, I forgot to mention those are sexable as day old chicks due to sex link traits.
Wait 5-6 weeks and post pics in "what breed or gender is this" section. You can usually tell by then on most breeds either through comb size/redness or color patterns. Sometimes stance will tell you sooner and hackles of roosters come in later.