Two regal second-half tries by full-back Jonny Burgess guided RBAI to their 27th Renault Ulster Schools' title on St Patrick's Day.
Ryan Caldwell after he received the cup from Prince Andrew
Underdogs Wallace looked to be heading for a major shock and grab their first title when they held a 10-3 lead five minutes into the second half.
But when RBAI's disciplined finally returned, and their line-out began to work efficiently, they buried Wallace in scoring 20 points without reply.
Fly-half Jonny Watt kicked 13 points with his opposite number Thomas Shorten adding a penalty to his conversion of Neil Annett's first-half touchdown.
It was a proud captain Ryan Caldwell who stepped up to receive the famous trophy from the Duke of York, who had earlier opening a disabled spectator enclose at Ravenhill.
Wallace gave the highly-fancied RBAI a real scare in that opening period with their big pack securing plenty of opposition to peg their opponents back in their ''22''.
RBAI 23 (3)
Tries: Burgess 2
Cons: Watt 2
Pens: Watt 3
Wallace High 10 (7)
Nerves, however, were getting to both sides with a number of errors spoiling a number of promising moves.
Shorten, twice and Watt were both off target with penalties before Wallace deservedly grabbed the lead in the 17th minute.
Great work by the pack in retaining possession and after a few drives to the line, it was scrum-half Annett who burrowed his way over with Shorten converting.
RBAI finally started to get back into the game and Watt cut the deficit with an excellently-struck penalty from the Wallace 10-metre line.
RBAI, however, failed to get into the rhythm that saw them swan through the earlier stages of the competition.
Wallace, though, just kept pegging away up front committing more players to the breakdown with Shorten continually putting the ball behind the RBAI defence.
Wallace began the second half the way they finished the first with the forwards driving and Shorten finding ground deep into Inst territory.
Shorten missed one good penalty chance in the 40th minute, but made up with sweet strike from 35 metres and Wallace were looking like the new champions.
RBAI looked out of the game, but suddenly they burst right back to level the scores in the 45th minute and moved on to deny Wallace their third attempt of glory.
Good possession by the RBAI pack allowed Watt who work a short inside pass to Burgess who burst through two tackles to score. Watt converted to square the game.
It was Watt who then gave Inst the lead for the first time in the 52nd minute after some great forward pressure.
Wallace were penalised and Watt stroked over a lovely penalty from a very acute angle.
Then came the deciding try with a smart piece of thinking by Burgess who kicked ahead into the gap, and the ball bounced kindly for the full-back to re-gather and score at the posts.
Watt again added the extra points and also added a penalty as Wallace's game began to fall apart.
Wallace tried to force the pace looking to back into the game, but made too many errors.
RBAI never allowed Wallace that same platform again, and the big Belfast institution were not to be denied their moment of glory in front of the first Royal visitor to the final in the 127th year of the competition.
RBAI: Jonny Burgess; Jesse Booth; Michael Simms, Michael McKeever, Richard Fegan; Jonny Watt, Philip Coulter; Aaron Burns,
Ryan Caldwell, capt, Clark Atkinson
Wallace High: Adam Tucker; Jonathan Currie;
Mark McCormick, Lloyd Jones, Darryl Clifford, Iain Semple; Thomas Shorten, Neill Annett;
Chris Henry, capt.
Replacements: Tom Fraser,
Referee: Marshall Kilgore (City of Derry).