Greens co-leader James Shaw said the decision to support the funding of a private green school "was an error of judgment" and that he apologised for it.

He's met with a variety of organisations, including schools groups and unions, and said he's taken the time to reflect on their concerns and to act on them.

This comes following days of criticism from the Greens' bases, as well as the National Party, over the fact the private Taranaki school got $11.7 million.

Shaw said every dollar of the $3 billion fund was spent to create jobs and one of the sectors most at risk from the downturn was infrastructure and construction.

He said this had knock-on effects for the local community.

Shaw said when the mayor of New Plymouth first told him about the greens school, he saw an opportunity to support a green infrastructure economy.

Shaw said it was "a fair question" to ask why the money was going to a private construction project when so many public schools were run down and mouldy.

He said this was why the Government had invested in school infrastructure late last year but it was apparent this money wasn't getting into schools fast enough.

He said their decades-long commitment to public education hadn't changed.

Shaw said progress towards a better future demanded tough choices and not every choice would be the right one, and for that Shaw apologised again.

He understands representatives of the green school had approached the Crown to work on a solution but ministers couldn't be seen to interfere with this.

Shaw said his preference was for the money to be provided as a loan to ensure the money would be paid back in full in the future.

There is a contracting relationship in place between the school and the Crown and Shaw said it wouldn't be appropriate as a minister to go into the details of that.

Shaw said the mayor was quite clear he wanted the project to proceed and the school said if it weren't for the grant, it wouldn't.

The advice from the Infrastructure Group gave it about 4.5 out of 5 but Treasury "went another way" but refused go into details of the Treasury advice.

Shaw said he spoke to his colleagues about whether it was possible to get the money back but the decision was made the agreement had been made in good faith.

The money for the school came from a $3 billion Government fund to provide money for "shovel ready" projects.

The funding was provided on the basis it was an infrastructure project.

Shaw signed off the funding – this is despite the fact that the Greens have a policy stating that the Government should not give money to private schools.

Green Party members have been highly critical of this decision and Shaw has come under intense pressure over the decision.

And it's not just Greens members upset.

Yesterday, the Chair of the Taranaki Secondary Schools Principals' Association (TSSPA) Martin Chamberlain published an open letter to Education Minister Chris Hipkins.

"Our members are united in their opposition to the recent 'shovel ready' funding decision in favour of the local Green School," it said.

"We cannot accept taxpayer funding being directed to individuals who will privately own the expanded asset and profit from the venture."

The TSSPA called for a full retraction of any fund or loan offer.

This morning, National leader Judith Collins said if a contract to the school has not been signed, the funding offer needed to be withdrawn.

She was critical of the fact this school was getting Government money, when other schools in the Taranaki region are facing financial difficulty.