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.