Port Ahuriri School announced a $3 million refurbishment during its 150th anniversary celebrations at the weekend.
More than 250 people gathered at Port Ahuriri School on Saturday for an official opening, school tour, memorabilia display and picnic.
Principal Glenn France said he announced plans for a $3m Ministry of Education refurbishment of the school during his speech at the official opening.
He showed past pupils the plans and drawings for the "exciting" project, which is due to begin in May next year.
"It involves every single space in the school including the hall."
There would be significant extensions to the main block, all classrooms would be turned into innovative learning spaces, one block would be demolished and another would be refurbished and moved, he said.
The whole project is expected to take 18 months.
Mayor Bill Dalton also spoke at the event and one of the oldest students, a 96-year-old, helped cut the celebration cake with current students.
The day was a great way for pupils from the 1930s to today to catch up and have an enjoyable time in the sun, he said.
"Being the oldest school in Napier City a huge number of Hawke's Bay residents have come through it.
"Everywhere you go people have a connection to Port Ahuriri School."
A 150th jubilee book will be released in about a month.