Wallace will face local rivals Friends’ in the McCullough Cup Final on Wednesday December 11, at their shared home ground Lisnagarvey.
Wallace progressed to the final thanks to a last-gasp winner from captain Ross Kelly.
They will go into the final as vourites to get their hands on Cup after a gap of 24 years.
The school hockey landscape has changed this year.
With the traditional powerhouses of Banbridge Academy and Cookstown High watching on as neither qualified for the semi-finals.
However, although many see Wallace as the team to beat this seasonm they were struggling to put away their chances in the first half against a stubborn Royal Belfast Academical Institution team.
The Lisburn boys, however, did take the lead.
A slick passing move ended with a ball played across the Inst goal and Daniel Nelson was left with a simple finish.
The lead was almost doubled midway through the half but Sean Murray brought a great save out Ulster under-18 goalkeeper Nathan Douglas.
Wallace missed another great chance to make it 2-0 minutes into the second half,.
Andrew O’Hare was one on one with Douglas but was crowded out by Inst defenders.
The Belfast boys made the home side pay for missing so many chances.
From a penalty corner, Patrick Fraser played a ball to Jonny Beckett who deflected into the top corner.
All of a sudden, the favourites Wallace were looking nervous, making errors and giving away possession in their own half.
But Wallace stayed strong in defence and the retook the lead with a great team goal.
Ulster under-18 star Sean Murray made a driving run through midfield, switched it to Daniel Nelson on the left, who crossed for Mark Acheson to put in on the slide.
Minutes later Inst were level again. Wallace gave the ball away on their own ‘25’, and the ball was ruthlessly put away by James Palmer.
In the last 10 minutes Wallace had two penalty corners awarded but were unable to convert from either.
In the final minutes Wallace captain Kelly fired his side back in front with a superb low dragflick that sent the crowd wild - and this time they did not allow Inst back.
Wallace made hard work of it but held on to make it an all Lisburn final - when all roads lead to Hillsborough.