The match threw up some drama right at the death as Tauranga peppered the Rotorua tryline, but they could not find a way through Rotorua's solid defence.
It means Rotorua keep their season alive for at least another week while Tauranga draw curtains on their season.
"Possibly there were a few opportunities we let go earlier in the game which came back to haunt us a bit but overall if you look back at where we were the first time we played them to now it has been a big improvement," said Tauranga Boys' College 1st XV co-coach Jason Spice.
"It's been a tough year for us but we came here with the idea that we could upset them and nearly did it.
"It was an honest performance from our boys and something they can be proud of."
Rotorua Boys' coach Ngarimu Simpkins said the match could have gone either way.
"I think it is good for Bay rugby to have a fitting final like that.
"We certainly didn't take Tauranga lightly, they just played really well today, and the match could have gone either way," he said.
Rotorua will represent the Bay during the race for a spot in the National Top 4 competition. They play the Waikato champions in Hamilton this weekend.
Rotorua Boys' High School 18 (James Tofa, Dorso Porima-Horne tries; Kaleb Trask con, 2 pen) Tauranga Boys' College 12 (Sam Takai 4 pen) HT: 3-6.
Final results
Bay of Plenty schoolboy finals on Saturday:
Baywide premier title:
Rotorua Boys' High School 18-12 Tauranga Boys' College
Division One:
Western Heights High School 40-34 Opotiki College
Division Two:
Katikati College 37-10 Taupo-nui-a-Tia College
Division Three:
Rotorua Lakes High School 20-15 Reporoa College
Under-15:
Rotorua Boys' High School 24-17 Tauranga Boys' College
