The Ombudsman's office found Associate Education Minister John Banks wrongly withheld information about how proposed charter schools would be funded.
The Post Primary Teachers Association made a request under the Official Information Act (OIA) about resourcing, capital and operating funding for charter schools. The information was withheld in February last year.
Ombudsman David McGee has recommended that Mr Banks release the information.
He advised that there was no good reason to withhold information on the funding of charter schools.
"The proposal to create a new type of school within the New Zealand educational system is a significant step, and is - in my opinion - a circumstance in which the disclosure of policy advice at this stage in the process is required by section 5 of the OIA when considering the accountability and participation purposes of this enactment.