RBAI beat Wallace High School 15-0 in the final of the Northern Bank Schools' Cup at Ravenhill on Monday afternoon.
RBAI players celebrate their Schools' Cup win
A 13th minute try by Inst flanker Jamie Lusk made it 5-0 at half-time and Patrick Irwin added a 43rd minute penalty to extend his side's advantage.
Andy Bryans and winger Irwin went close to scoring tries before Irwin accepted a Nick Dempsey pass and touched down on 63 minutes for his side's second try.
Irwin added the conversion to secure RBAI's 29th Schools' Cup success.
Lusk showed some neat football skills before charging over for the opening try to put his side in control.
Irwin missed the conversion and a first half penalty attempt but made up for that by scoring all of his team's second half points.
RBAI coach Gavin Monteith said he was pleased that his team adapted to the blustery conditions.
"We planned well, made the right decisions and when we went 8-0 ahead, that gave us a bit of breathing space. Irwin's try was the icing on the cake."
"We went out and gave it our all and our defence played well to keep Wallace out for the whole match," added captain Mark Jones.
Wallace skipper Gary Crowe said he was "very disappointed" but added that "nerves had played a part".
"We tried hard but the conditions were difficult, Inst executed their gameplan very well and they deserved to win," he added.