It was Connacht who got off the mark with a Callum Bolland penalty after just couple of minutes.
This was followed swiftly by a Jack Vaughan try, which was converted by Bolland, who also added another penalty before half-time to leave Leinster trailing 13-0 at the break.
That was the way the score remained despite both teams having scoring opportunities.
Connacht ran out deserved winners and having already accounted for Ulster and Munster, they lifted the coveted Youth Interprovincial trophy on their home patch.
Congratulations to all the players and team manager Johnny Brennan, who had Gerry Conway (assistant manager), Tony Dolan and Paul Flanagan (coaches) and Sarah Brennan (physio) as part of his backroom team.
Commenting on the Youths' success, Connacht's Domestic Rugby Manager Martin Gallagher said: "To the management and coaches who looked after these players - they must be complemented on their exemplary dedication to ensuring that the team performed and won all three Interprovincial games.
"Age-grade rugby in the province will be enhanced by the team's performance and wins and we must now build on this over the years to come."
For the record, this was the winning Connacht squad on the day - Callum Bolland (Buccaneers); Christopher Feeney (Galwegians), Jack Vaughan (Connemara), Andrew Fallon (Galwegians), Joe Keane (Westport); Jack Carty (Buccaneers), Barry Digby (Buccaneers); Daniel Moloney (Corinthians), Gary McConnell (Creggs), John Gill (Westport), Connor Kindergan (Monivea), Eoin Tarmey (Galwegians), Jamie Dever (Westport), Aaron Conneely (Corinthians) (capt), Daniel Qualter (Buccaneers).
Replacements: Oisin Tierney (Corinthians), Damien McNelis (Monivea), Diarmud Higgins (Ballinasloe), David Heath (Sligo), Lorcan Laheen (Monivea), Ronan Burke (Galwegians), Oskar van der Grijn (Sligo).
Meanwhile, the Connacht Open Day, which was held at the Sportsground on Saturday with the U-18 Interpro game as the centrepiece, was a huge success with fine weather and a great turnout.
Martin Gallagher said: "The weather was terrific and certainly provided us with a platform for the youngsters to come out and meet the Connacht players, who were on a high after their performance and win over the Cardiff Blues.
"It was an excellent turnout of children and watching them join in with their heros was a wonderful experience, there were smiles all round!
"I am most grateful to the professional squad and staff, especially John Muldoon and Michael Bradley, for their enthusiasm and commitment to ensuring that Connacht Domestic Rugby had a great Open Day."