I ordered size large for my large footed 11 year old.  He wears size 7 shoes and these are a bit too small.  This is a surprise because we've bought about 6 packages of these very same socks and they fit fine (and no, his foot size didn't change.)

We've been buying these Hanes socks for ages.  My boys go through socks like crazy.  These aren't super durable but they are cheap, so we just keep replacing them as necessary when they wear through them.  They stay up and the boys say they are comfy.

My favorite feature is actually that each different size has different color writing on the toes.  Why does this matter?  Well I have different kids with different sizes, and it makes it much easier to match the socks up when they come out of the laundry.