McGlashan led 17-0 at the break and went on to achieve its biggest winning margin in the four years of the Highlanders First XV competition.
McGlashan got on top in the forwards through the lineout work of lock Braden Jane and by the aggression of captain and No 8 Cameron Wood at the breakdown.
When the ball was moved wide, McGlashan had too much pace, and winger Robert Jopp and fullback Chris O'Connell each scored two tries.
The McGlashan back play was efficiently directed by halfback Ed Davies.
Fullback Mackenzie Haugh started the scoring with a drop goal and ended the game with a penalty goal when King's High School narrowly beat South Otago High School 30-27 in Balclutha.
The strong South Otago pack, led by No 8 Garth Devereux and blindside flanker Shane Calder, had given the home side a 22-15 lead at the break.
This was extended to 27-15 early in the second spell before King's started its late rally.
Centre Robert Peseta led the charge by scoring two tries and he was backed by lock Ben Williams, openside flanker Sam Keane and hooker Ben McKinlay.
The best of the South Otago backs were wing Jackson Cooke and halfback Caleb Edwards.
Waitaki Boys' High School led 17-13 at halftime but rallied in the second spell to score four more tries and beat Menzies College 41-13.
The best player was fullback Jamie Robb, who used his counter-attacking skills to score two tries.
The other key player in the backs was Levi Fogarty in the midfield, while openside flanker Jake Rhodes had a dynamic game in the forwards.
Winger Nathan Frisby scored five of Southland Boys' High School's 16 tries when Kavanagh College was beaten 104-0 in Invercargill.
Mike Molloy, on the other wing, scored three tries and Hayden Pope kicked 12 conversions.
Southland Boys' joins Otago Boys' High School as the two teams that have scored more than 100 points in a game in the Highlanders competition this season.
In other games, Gore High School beat St Kevin's College 50-14, and Otago Boys' beat Dunstan High School 57-3.
