It started off with the Fianna Fáil leader raising concerns about St Gabriel's Special School in Bishopstown in his native Cork.
A new school building is needed. The existing one is in such bad repair that the parents are now crowd-funding to make the school habitable.
The Taoiseach said the Government is committed to investing €10 billion in education. This includes a lot of investment in school buildings.
Even in the wealthiest countries, governments cannot do everything they want to do in one year, said Leo Varadkar. Projects must be prioritised.
And that's where the spat kicked off.
TROUBLE IN PARADISE?: As @MichealMartinTD & @campaignforleo have a spat over spending priorities, @MaryLouMcDonald claims "There's trouble in paradise. The Government parties have fallen out with each other here before our very eyes." pic.twitter.com/wWNO10xZhO
— RTÉ Politics (@rtepolitics) April 25, 2018
The Taoiseach pointed out that he has heard Fianna Fáil's education spokesperson Thomas Byrne "one day demanding more spending on new school buildings, the next day demanding full pay equality for teachers, the next day demanding an increase in capitation."
He said that "all that does not add up...all of those things cannot be delivered in one year so which is your priority? What would Fianna Fáil put first?"
Fianna Fáil leader Micheál Martin reminded the Taoiseach of the unique deal that is keeping Fine Gael in power.
He said his party put its priorities into the Confidence and Supply deal. He claimed the reduction in pupil-teacher ratio would not have happened if it was not put into the deal and "you guys resisted it."
The Taoiseach said the agreement "was not resisted. It was agreed. It was a negotiation and as is the case in any negotiation, you try to agree what is possible and you try to cut your cloth to meet its measure".
Then came this jibe from the Taoiseach to Fianna Fáil - "What is wholly dishonest in politics is going around the country promising every interest group that you will do everything they ask and you will do it this year because that is not possible."
Fianna Fáil has consistently said it will honour its deal with Fine Gael and support a third budget this October. But battle lines were certainly drawn today.
As the spat between Mícheál Martin and Leo Varadker concluded, Sinn Féin leader Mary Lou McDonald seized on it and interjected: "There's trouble in paradise. The Government parties have fallen out with each other here before our very eyes."
One of the most telling lines from today's exchange came from the Taoiseach when he told Mr Martin: "I am keeping a record of this as the weeks go by. All of the things your spokespeople are promising, hundreds of millions of extra spending every week for every interest. That is exactly the kind of philosophy that landed this country in the hole that we had to take it out of."
Expect that list the Taoiseach is keeping to resurface during the Leaders' Debates in the next general election, whenever that is.
It may be a stretch to say there is "trouble in paradise".
The awkward Confidence and Supply arrangement could not realistically be dubbed 'paradise'.
But battle lines are being drawn.
