I usually just lurk here, but I have to admit, thoughtful, purposeful selective breeding is highly relevant to my interests, so I had to butt in here. I'll preface all this by saying I'm no experienced breeder (I own 4 hens and have only had them a few months!!) nor am I exceptionally experienced with chickens in specific, but selective breeding has been an interest of mine for years and I've spent considerable time researching it.
I noticed that TaraBellaBirds said
Again, I'm not an expert here, but I've experienced a similar problem dealing with rats (I used to breed them as pets and feeders for my pet snakes). I selected my rats primarily for personality--they're nowhere near as big as a roo, but a vicious rat can make you need some stitches. Personal experience here--so any rat which displayed bad personality traits was, shall we say, disposed of. I didn't want them breeding and passing along any aggressive traits they had, and couldn't risk unwanted babies, and so had a series of 'grow-out pens'. Now, this probably would have to be modified for chickens due to the fact that you can have a bachelor 'pad' of rats--but definitely not of roosters...but the principle remains.
For simplicity's sake, I'm going to define a few terms for my use so there's no confusion.
Grow-outs will be chicks or young adults which have not yet proven whether or not they are worth keeping as breeding animals--whatever you are breeding for.
Breeders are adult animals that clearly have a place within your breeding program, and whose genetics you want to see in future offspring.
This would require a few pens--which may be a huge pain, but would allow you to track your genetics much, much more closely than a single pen. Might not work to everyone due to expense and space, but I think it's the optimal setup for this sort of thing.
You'd have one or two Breeder pens, and no young animals would ever be introduced to these pens unless you are absolutely certain that you want those genetics in the long-run.
You'd have a few Grow-out pens where you'd keep each generation of chicks, and you could observe them until you have identified those birds you want to keep and put in your Breeder pen(s) versus those who get sent to freezer-camp or sold on as pet-quality birds, or whatever you do with your extras. These pens may even contain birds old enough to be producing fertile eggs--which would not ever be hatched. These eggs would be delicious omelettes or devilled eggs or bread or cookies or something equally lovely. The roos who'd end up in freezer camp could have all the time they'd need to grow big and their faulty genetics would never be allowed into your breeding stock--simply quarantine your keeper hens for a few weeks until any sperm they may be retaining can work its way out of their systems.
Is that in any way feasible? I think it'd take a little while longer than just tossing together a roo and a hen and hoping for the best, but I don't think that's what you're going for here.
Has anybody put thought into selecting for hens whose temperament is desirable as well? I only have 4 birds, but I think of the group only one or two would be animals I'd want to use in a selective breeding program, despite how simply gorgeous they are, for reasons of skittishness. I know generally speaking the rule among chickens (actually, among almost all animals being bred) seems to be 'the more hens the better' with little regard to female quality, whereas male quality is highly focused upon, but to me to have a good baby, both parents need to be equally scrutinized for quality.
Annnnd this is a novel...sorry everyone!