He said if the Government had gone ahead with the policy it would have intensified public opposition and the decision was driven by the debate with parents being lost.
"What it risked doing was causing months of industrial action, huge amounts of anxiety from parents and children and you've got to ask yourself is if that's really worth it and I think the conclusion we drew was no."
Mr Key defended the advice the Government had been given over class sizes.
He said the Government was advised that money would be better spent on improving the quality of teaching and not raising the number of teaching beyond the 52,000 teachers and principals currently employed.
"In the end the advice we had was having built up the stock considerably, it's better to spend it on the teaching quality, and that's a fair enough argument."
Mr Key said the Government was still committed to improving teacher quality but would find a new way.
Labour education spokeswoman Nanaia Mahuta said Mrs Parata should spell out her plan for improving teacher quality and student achievement.
"This shouldn't be difficult. The minister has trumpeted this as her primary goal," she said.