UPDATED 9.59am: School principals blame a lack of clarity around funding for cutbacks in some classrooms.

Tighter rules are restricting what schools can ask parents for a contribution towards.

Rangitoto College principal David Hodge says the Education Ministry isn't clear about what it pays for, what it's not paying for, and who makes up the difference.

"What really annoys principals is that the ministry won't be absolutely clear.

"They make generalised statements by saying there's enough money in the budget, but they won't actually be transparent about that."

Hodge says on the one hand the ministry encourages IT courses, but it only covers 16 percent of the cost.

"And according to their rules at the moment we cannot ask parents to contribute towards that.

"All I'm asking for is that the ministry open up the books and are really transparent about what they fund and what they don't fund."