Minister of Education Hekia Parata announces her decision to co-locate Marlborough Boys' and Marlborough Girls' College on a new site.

Blenheim's colleges are to become two single-sex schools on one site, costing $63 million.

The Marlborough Boys' and Marlborough Girls' Colleges will be co-located on a new greenfields site from 2021.

Education Minister Hekia Parata made the announcement at a special assembly at Marlborough Girls' College on Friday morning.

DEREK FLYNN/FAIRFAX NZ The Marlborough Boys' College in Blenheim.

A site for the schools has yet to be decided.

The existing schools had old and leaky buildings that required major upgrades.

Public consultation around the schools' future began in 2013. The ministry last year said there were three options; two schools side by side on one site with a possible tertiary addition, a co-educational college and repairing the existing schools.

Students and staff from both schools attended the assembly on Friday.

Marlborough Girls' College principal Karen Stewart said she was "very excited" about the decision and that it was a "wonderful opportunity" for Marlborough's young people.

The schools needed to discuss what the learning program was going to look like before a site was decided, she said.

Marlborough Girls' College was going to get some moveable classrooms to replace its leaky library, and those could possibly be used in the new development, she said.

She only learned of the decision on the morning of the announcement.

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Marlborough Boys' College principal Wayne Hegarty said he understood the $63m development would not include land costs. He thought there would be discussions about adding a tertiary addition to the site as well.

"Whatever the decision was, it was going to present its own unique challenges, but it's a wonderful opportunity for us," he said.

Parata said the development would give the schools an option to run some classes collaboratively, but that was something they would have to decide.

"This is pretty exciting for New Zealand, not just for Marlborough," she said.

Kaikoura MP Stuart Smith said the decision to co-locate the schools, with a combined roll of 1900 students, had secured their future.

The history of Marlborough Boys' College, which had buildings more than 100-years-old, would be preserved, he said.

"The two schools will be co-located at a new $63 million development. They will both use the state-of-the-art buildings and technology, while working together to improve the achievement of their pupils," Smith said.

"By having two schools on one site it opens the opportunity for a wider range of subjects to be taught, and the schools could look to offer tertiary level courses.

"The decision to move the two colleges to a new site is wonderful news for students, parents, and teachers."

The decision to co-locate was supported by the principals of both schools and went through a rigorous community consultation process, Smith said.

There were 620 submissions from the public, with the majority favouring two schools on one site, he said.

"It is important the new site acknowledges the history of the colleges while future-proofing the schools against population growth.

"I am delighted Marlborough is receiving this major investment and will work with the minister to find the best site for the two colleges."

The next step was for the Ministry of Education to secure a suitable site for the development, and the public would be kept informed as work progressed, Smith said.

He had "some ideas" about possible sites but it had to be a community decision, he said.