Campbell College are favourites to win the Danske Bank Medallion Shield but first have to overcome RBAI in the semi-final at Shaw's Bridge today (11am).
Campbell, like Inst, have swept through the last two rounds with a morale boosting 10-5 victory over old rivals Methody before a 34-5 win at Sullivan Upper.
The Osborne Park team disposed of Bangor Grammar 26-5 and then Ballyclare High 34-5.
Campbell, who have nine players in the Ulster Schools squad, will be at full strength. Captain Marcus Collim is a converted back row forward now playing at prop and is destined for a bright future.
Justin Savage, Johnny Haldane and Josh Haslett have all scored a brace of tries while No 8 Jack Barry-Glendinning was outstanding against Sullivan.
Inst have an attacking full-back in Conor Field who has already scored three times while flanker Charlie Fryars has two tries.
But even though Inst have home advantage, Campbell should qualify for the final.
Campbell's Johnny Cubitt said: "We are strong defensively but Inst have an effective back line so we will need to be wary."
In the other semi-final there should be little between Wallace High and Coleraine Inst in Lisburn (10.45am), though home advantage could just give the former the edge.
• CRAIGAVON'S 35-20 Danske Bank High Schools' Trophy win over Omagh sets up a semi-final showdown with Ballynahinch.
The teams drew 5-5 at Omagh last week on a heavy pitch but there was more entertaining rugby yesterday.
Craigavon No 8 Jamie Dickson scored two tries, John Aston and Thomas Neill also touching down, with Josh Newell converting three and adding three penalties.
Dromore take on Slemish in the other semi-final.