The Union flag and the Tricolour were flying side by side over the entrance and in the hall of St Aidan's CBS in Whitehall, Bertie Ahern's alma mater. "I never thought I'd see the day," one Department of Education official said.
The computer teacher, Ray O'Neill, acting as MC, said Dublin had not seen anything quite like it since Queen Victoria visited Castleknock College nearly a century ago.
The Taoiseach told the cheering boys he was delighted to be back in his old school and "to introduce my good friend, Tony Blair, to you".
There were friends and neighbours everywhere. The ostensible reason the two prime ministers were visiting St Aidan's was to launch a programme to link schools on both sides of the border through the Internet. Dell Computers and Telecom Eireann installed a video conference link for the occasion.
At the other end of the link were students from Carrigaline Community School in Cork, Loreto Grammar School in Omagh, and Limavady Grammar School in Co Derry. Eireann chief executive Alfie Kane's strongly Presbyterian home town.
Mr Blair's main theme for the day was the power of education, and more particularly, technology in education. Information and communication technologies were "a tremendous gift" - they allowed young people in particular to open out in dialogue to other cultures and nations, to understand them better, to banish ignorance and hatred, to enrich diversity.
When it came to questioning the two leaders, the Whitehall boys wanted to talk about one thing: football, whether in its Gaelic or Association forms. The Taoiseach ventured into the realm of real controversy by saying Dublin would not win an All-Ireland until they found a fullback line who were a foot taller.
Mr Blair fully approved of Duncan Ferguson's transfer to his beloved Newcastle United, although he admitted he tended to see football in "black-and-white terms".
Across the video link - in between moments of screeching feedback - it was left to the Northern students to ask the hard questions. A girl from Limavady asked if the prime minister envisaged a united Ireland in his lifetime.
No, he did not, and he had said so as long ago as May of last year, a few weeks after taking office. But what he and Bertie Ahern thought was not important. What was important was that under the principle of consent, enshrined in the Belfast Agreement, it was up to the people of Northern Ireland to "state their view" on whether there should be a united Ireland or the North should remain part of the United Kingdom.
A Limavady boy asked Bertie Ahern why unionists should trust him, given his belief in unity within his lifetime. They should trust him because, whatever his own aspiration was, he had asked the people of the Republic "to remove the constitutional threat perceived by unionists and others that we would interfere with their democratic wishes". Whatever the wishes of the people of the North were, the people and Government of the Republic would "abide by them".
Alan Sherlock (17) from Santry, one of the St Aidan's questioners, thought it was amazing and wonderful the leaders of two countries who not so long ago were "almost at war sometimes" could now come together as friends and work for peace.
St Aidan's motto, Pax et Spes, Peace and Hope, was "a pretty good motto for anyone", Tony Blair said as he left the hall. But the cheers this time were for the Taoiseach, as he announced, with the backing of the Minister for Education, Micheal Martin, sitting behind him, that the school could have the rest of the day off.