One of the things that really strikes me when you look at the line-ups for Academy games is that relatively few make it through and end up playing professionally.
Compare and contrast - as my old exam papers used to say - the Northern Intermediate League Cup Final from April, 1964. Leeds: Harvey, Smith, Wright, Greenhoff, Madeley, Gray, Bates, Johnson, Belfitt, Lorimer, Lowery. The Blades: Walton, Badger, Shaw B, Munks, Bell, Clarke, Woodward, Wagstaff, Birchenall, Barlow, Disney.
The vast majority broke through to play first team football, some at a very high level indeed.