MANY still query the theory, but Cork U-21 football boss John Cleary is absolutely convinced of the direct correlation between success at that grade and future senior All-Irelands.
It certainly seems to work for the Rebel footballers, whose burgeoning underage stars take on Cavan in tomorrow's double-header of Cadbury's All-Ireland U-21 semi-finals in Tullamore.
"If you look at Cork's (senior) success in 2010, we had won U-21s in 2009 and 2007, and I think 11 of those players were part of the senior team," he noted.
"Look at Dublin, they've won two of the last three U-21s and their senior win in 2011 came directly after an U-21 title in 2010.
"Even Donegal show it – they came within the width of a crossbar of winning the U-21 title in 2010."
Sceptics will produce other statistics, like Galway's seniors' inability to kick on after winning U-21 All-Irelands in 2002, 2005 and 2011, but Cleary remains convinced of the direct connection.
"If players win at U-21 level, then when it comes to senior they think 'oh, we've played these lads before and beaten them'," he said.
"They're just not afraid of anyone they come up against and I really think an awful lot of it is about the confidence that U-21 success gives them."
Cork have certainly harnessed their underage talent to a remarkable degree recently.
Like tomorrow's opponents, they are three-in-a-row U-21 champions in their province and, in his earlier guise as a selector, Cleary was part of an U-21 management which won four Munster consecutive titles from 2004-07.
But what is remarkable is the amount of their top minors that Cork are managing to keep involved at the elite level.
In 2010 Cork's minors were pipped by Tyrone in the All-Ireland final, and nearly a dozen of that team are now part of their U-21 squad.
When they beat Tipp in the recent Munster U-21 final they had nine players – David Hanrahan, Damien Cahalane, Alan Cronin, Jamie Wall, Tom Clancy, Mark Sugrue, John O'Rourke, Dan McEoin and Brian Hurley – who started the 2010 All-Ireland minor final.
That high level of continuity is unusual and Cleary said that it is part of their management strategy.
"We brought eight of those 2010 minors into the U-21s the following year and four of them (Cahalane, Cronin, Wall and O'Rourke) played," he explained.
"We try and work with a full panel of 30. The last three or four of them might be straight out of minors and mightn't even get a game in their first U-21 season, but we bring them in as quickly as possible to try and maintain that continuity and keep them progressing."
Yet despite bidding to reach their fourth All-Ireland U-21 final in the past eight years, this current Cork team have never previously met Cavan, not even in a challenge game, which makes them particularly wary.