Groups representing secondary principals and teachers are disappointed critical information about a private high school's bid to become a state school is being kept under wraps.
The Office of the Ombudsmen has backed a Government decision to withhold information, including an assessment of the likely impact on other schools if Wanganui Collegiate becomes part of the state system.
It says publishing the information might harm the Education Minister's ability to consider further advice before making a decision in August this year.
The Secondary Principals Association and the Post Primary Teachers Association say the decision is unusual and the information should be public.
PPTA president Robin Duff believes teachers need to know if the ministry thinks allowing Wanganui Collegiate to integrate will harm other schools.
"If there's to be a free, frank and open discussion about the introduction of another school into a situation where the area is quite adequately supplied for schools - then information about those details are essential."
Both groups say the public should know the likely impact of the school integrating, lowering its fees and accepting a maximum roll of 400 students.