The funding announcement was received with loud applause.
The visit came the day after a One News Colmar Brunton poll showing English's National Party was behind Labour under Jacinda Ardern.
English's speech was more personal than his usual campaign speech, beginning with an extended mihi in Te Reo Maori. "I'm proud to be your Prime Minister," he said, before speaking to the students of his own background.
He spoke of his large extended family - drawing gasps of astonishment at the numbers of children involved - and told them his Samoan matai title, reeling it off at speed and earning himself a round of applause.
"Almost anything that can happen to a young man in New Zealand has happened in that family," English said.
He knew of the "potholes" young people could fall in on the way, but said young people were more confident than his generation, and better at understanding differences.
"Each one of you matters. Certainly to your family, to your school and you matter to me."
Kaye said it was a pleasure to be at Whangarei Boys' High, saying she had visited Northland College more than any other school and Whangarei Boys' had finally said to her "when are you going to show us the love?"
She too spoke of her personal experiences, including the breast cancer she battled last year. She told them that taught her the value of strong friendships.
"So choose your friends well."
She urged the boys to make the most of life, saying one of the people she admired most was a Northlander - Dr Lance O'Sullivan from Kaitaia.
"We need more Lance O'Sullivans."
Principal Karen Gilbert-Smith said the much-needed redevelopment would give the school modern work spaces rather than those of 60 years ago.
Other schools tagged for public-private partnership redevelopment include Scott Point Primary in Auckland and the co-location of Marlborough Boys' and Marlborough Girls' Colleges. Associate Education Minister Tim McIndoe said PPPs can provide significant cost savings and efficiency gains. "These projects could benefit from such a model, should we choose to proceed this way."