I think all flocks are a bit different and it may depend a bit on the makeup of the flock. I got my 1st batch of 8 girl chicks last April - 2 ea of RIRs, Australorps, Stars & EEs. I really didn't notice any pecking at all, though there was a bit of chest bumping - the RIRs were the pushiest. DH and I thought that somehow we had such a well adjusted flock that they wouldn't even need a pecking order. Hah! We moved them outside at about 4 weeks and still no major fighting - until one day when I was offering some weed treats to them and bang, one of the Stars pecked the other on the head hard. I was devastated! So from there the real pecking order began to shake out. It's painful to watch, but no one actually drew blood. It was more of a chasing and pecking on the head thing. Sometimes they would go at each other chest to chest. Just keep an eye on the bottom ones to make sure they have access to food and water - sometimes the top ones won't allow them to eat. I always keep food & water in 2 locations just to make sure everyone gets a turn. So, now that they are grown, the order has remained much the same with the Reds on top and they rarely peck or chase each other since everyone sort of knows their place. I'm getting some more this April so I'll have to go through the process again when they are old enough to merge together. Also, I have read that if one or two are really mean to the point of causing injury to the others, you should separate the thugs from the others for a while. Supposedly when you return them to the flock, they will have been bumped down the pecking order. I have never had to do this so I don't know if it works, but it sems to make sense.
Good luck, I think giving them as much room as possible helps reduce pecking stress too. I always let mine out for about an hr. of supervised play each evening which they really love.