Wallace got off to the ideal start in the contest, after scoring on their first attack into the BRA 22.
Fly-half, Quinn Armstrong, showed excellent awareness to dive over into space beside the posts for the early score.
Full-back, Josh Geddis, added the extra two points from the tee.
BRA pushed into the Wallace 22 hoping to get back on level terms, however Wallace were excellent in defence and forced the Belfast side back.
Wallace celebrated their second try after another attack around 20 minutes into the game. This time it was their captain, flanker Jon Rodgers who powered over shortly after a 5m penalty.
The try was good reward for the attacking play from Wallace, who were powerful in their carrying and accurate in passing.
BRA gave themselves hope before HT, with the lively scrum-half, Connor McVicker, showing quick reactions to pick and go from a ruck at the tryline. He converted his own try to go into the break behind by a converted score.
In a cagey opening to the second half, both sides were fighting to get the upper hand in field position and possession. Both sides looked to test their opposition's backline, with high balls testing their handling in the backfield.
Belfast Royal Academy then scored their second of the contest, after McVicker showed invention to chip a smart ball through in behind the Wallace defence. He found his half-back partner, skipper Frank Davis, who had the speed to ground the ball for the try.
Wallace then showed an excellent response, with the powerful prop, Rio McDonagh, crashing over the tryline from close range.
The try was the result of a superb charge down block from lock, Rhys Ewing, keeping BRA under pressure deep inside their 22.
Geddis converted the try for a lead of 21-12.
BRA kept probing for a way back into the game and decided to take a penalty from just outside the Wallace 22. Connor McVicker slotting the kick to narrow the scoreline to 21-15.
Wallace quickly turned defence into attack, and scored their fourth try from an attacking lineout. Lock, Michael McCavery, getting the match-ending score.
The conversion from Geddis brought the contest to an end and the Wallace team sprinted towards their supporters in the Nevin Spence Memorial Stand to celebrate their achievement.
Wallace will meet Royal School Armagh in next month's final, which will be a special occasion for both after the 2020 Danske Bank Schools Cup between the two schools had to be cancelled after Covid-19.
Scorers
Wallace High School:
TRY: Armstrong, McVicker, McDonagh, McCavery
CON: Geddis x4
Belfast Royal Academy:
TRY: McVicker, Davis
CON: McVicker
PEN: McVicker
Teams
Wallace High School:
(1-8) Rio McDonagh, James Gould, Ollie Fitzsimmons, Rhys Ewing, Michael McCavery, Ben Moore, Jon Rodgers (Capt.), Sam Warwick
(15-9) Josh Geddis, Daniel Wilson, Luke Dillon, Harry Daniel, Joshua Booth, Quinn Armstrong, Alex Stevenson
Replacements: Odhran Cole, Daniel Macklin-Copeland, James Furphy, Charlie Thompson, James Curran, Corey Dawson-Stirling, Elliot Harris.
Belfast Royal Academy:
(1-8) Elias Agbonkpolor, Aaron Caldwell, Hadwyn Hughes, Luke Houston, Jayden Irwin, Zach Archer, Oliver Cox, Ryan Calwell
(15-9) Adam Hewitt, Caleb McWhinney, Jake Carpenter, Max McKittrick, Alex French, Frank Davis (Capt), Connor McVicker
Replacements: Nathan Rossal, Charley Maxwell, Noah Gregg, Sam Saunders, Elijah Fitzpatrick, Evan Lemon, Ruben Gourley, Lorcan Bell
