Jeremy King was about to settle in for his Father's Day bacon and eggs when he was alerted to the burglar alarm going off at Glen Massey School, near Ngaruawahia.
Leaving breakfast behind, he grabbed son Jabin, 11, and headed to investigate.
Jabin was the first to notice smoke billowing out of the school's 100-year-old classroom.
Mr King, who is on the school's board of trustees and is also on the security monitoring team, called 111 as Jabin grabbed a fire extinguisher.
"He kept a cool head, he got a fire extinguisher while I was ringing 111, we tried that and it lasted about three seconds so we got the hoses after that. [Jabin] was on the ball. "
Resident Roger Edgecombe and his partner were next at the scene, and said if it was not for Mr King's quick actions the damage would have been a lot worse.
"Him and his young fella were doing bloody well, actually ... If he hadn't have been there we wouldn't have had a school."
Waikato fire investigator Kevin Holmes confirmed the fire was suspicious and said the building suffered moderate damage.
"It started outside and burned up the wall and into the ceiling. Once [fire] got in the building it set off the burglar alarms."
School principal Tim Howard said damage was confined to their much-loved 100-year-old classroom, which also had three of its small windows smashed on Saturday morning, the sixth episode of vandalism at the school since March.
Fortunately for the school, Mr Howard believed the classroom would be able to be saved but said the school would close today and tomorrow as they looked for an alternative room.
The fire began outside the classroom with an item being lit near the rear entrance.
"We've had issues with vandalism with broken windows and there was another incident on Saturday morning and my initial thought was that it may be related and it might still be."
Mr Howard thanked Mr King and others for rushing to the school's aid.
"They're all local and have been through the school, it's their school."