Replacement lock Shequelle McKay helped spoil Tu Toa's lineouts, and the high school took advantage to put on a slick move in which right winger Shayden Pirikikahu-Phillips carved through to score on his opposite wing.
"Three trainings a week pays off against a heavier pack, and showing hearts of lions," said Malcolm.
Hooker Jack Van Bussell led the way as Wanganui High looked to hang on to their lead.
Keanu Puki-kaa, Kayden Shedlock and Villimoni Koroi came off the bench to make an impact and blindside flanker Fagen Lemalie stepped his way through the defence to dot down, with Sam Malcolm converting for 24-13.
Tu Toa grabbed a consolation try in the dying minutes when they ran wide and scored at the corner flag. Darryl Malcolm also said No8 Sam Adams and lock Danyon Barr were worthy of mention.
The high school team next have a co-ed competition game away to Hawera High School tomorrow.
Back from their jaunt to Nelson for the quadrangular tournament, Wanganui Collegiate First XV will have their rescheduled home game against Lindisfarne this Saturday.
After virtual non-stop rugby of twice-a-week games in June/July, followed by their Australian and Nelson tours, coach Guy Lennox said it was good to balance out their remaining five or six matches of the season: "It's not that suicidal stuff we were doing earlier."
Collegiate will play through to their last game, against New Plymouth Boys High, in September.