You are spot on they call it "polishing the diamond" United will never admit to this but it is exactly what they do
They have a programme that they call MANUS (can't remember off top of my head what it stands for) where they select usually 3 or 4 from each age bracket that they feel are exceptional at at least one thing, be it speed, technically exceptional, athletic ability, aggression, physical attributes, two footed etc, nothing scientific any thing anyone can see in players if you happen to watch them enough, they also look at a boy's parents and siblings is there an athlete, ex pro, or pro sportsmen in the family so genetics are looked at (this is the case with every club)
The selected lads then go to Ashton on Mersey school where they are educated and taken out of school in the mornings or afternoons and coached at Carrington (classed as full time) so the hours in touch with the coaches doubles in comparison with the lads who are just coached at night (classed as part time) so how is a boy who is coached just for 6 hours a week going to compete with a boy who is coached for 20hours a week it's impossible add to this gym sessions, fed the right foods as they are fed by the club when there and so on they are also lodged by United by host families and it soon becomes clear there is a two tier system in place, it's like someone driving round a race track in a car with all the extras turbos and what have you and you getting the 1.1 litre version and being expected to keep up, it's impossible
The difference with Uniteds approach and City's are obvious, if you are in City's academy squad you are all on the same level, you are all schooled, you all have the same contact hours with the club, etc etc this method allows for lads who aren't top of the pile now to have the time to catch up and sometimes surpas the kids at the top, it's a level playing field, developing kids is not an exact science kids grow at different rates some are nearly a year younger than the older lads in there age group and when you are 10/11/12 and so on that can be massive in terms of growth, mind etc City's way allows kids time to develop United's is more of we have these 4 we are hanging our hat on them very risky and flawed if you ask me
City do it right, the way we develop players allows every boy the chance to progress and be an equal if the boy doesn't make it he can't say he wasn't given the opportunities, the same can't be said of United