The first half of the match was a real arm wrestle as the home side took a slim 3-0 lead into the break, courtesy of a Brad Munro penalty.
A rev-up at halftime triggered a much better second half for Western Heights, as they piled on another 25 unanswered points. Hikairo Stewart-Reid got the ball rolling with a well-taken try off the back of the ruck.
Munro was kicking well as he slotted the conversion from out wide and also added two penalties early in the second period.
A chip kick down the right touchline took a wicked bounce and Dejae Adlam collected to score Heights' second try.
Liam Membery then scored the final try of the game when he plucked an intercept about 40m out from the try line, before scooting away to score under the posts. Aquinas had a late flurry of possession but could not find a way through Heights' defence.
Heights co-coach Steve Smith said it was special to pick up the Te Kani Shield. "It is the first time we have ever played for it, I think, well at least not for a long time anyway."
He said the team they had now were mainly Year 13 students. "It has been three years in the making," he said. "A lot of them were in the 1st XV at Year 11 when they were young, and we struggled."
Smith said they almost missed out on playing in the Bay of Plenty secondary schools first division this year.
They had to win a play-off game against the Tauranga Boys' College 2nd XV at the start of the year just to secure a spot.
Western Heights High School 28 (Hikairo Stewart-Reid, Dejae Adlam, Liam Membery tries; Brad Munro 2con, 3pen) Aquinas College 0. Halftime: 3-0.