The Scots then play Wales at Bridgend on Wednesday, the short recovery time after the Ireland game intended to simulate the quick turnaround between pool matches in the Junior World Championship. .
Fagerson, who finished his schooling at Strathallan, was a stand-out for Scotland Under-18s in their five-match international programme and became one of three younger players selected for the Scotland Under-20 squad. He is joined by the Strathallan back-row Jamie Ritchie and the Northampton Saints Academy stand-off Rory Hutchison.
Ritchie, who moved from Madras College to Strathallan, is a gifted sportsman who has gained honours in judo and cricket and who is versatile in rugby. But Sean Lineen, the coach, thinks Ritchie's athleticism is suited to being close to the ball. "We'll play him in the back row" said Lineen.
In addition to bringing in under-18 players, Lineen has access to a trio of Scotland Sevens caps, centres Chris Dean and Neil Herron and scrum half Alex Glashan.
He will name his starting XV later today.