After a realisation that some intermediate schools could lose up to nine teachers, the Government capped losses at no more than two over three years.
Mr Key was in Europe as protest against the policy intensified but was on the conference call with Ms Parata and senior National ministers that decided to spike the policy.
He said he would describe the idea of teacher "quality over quantity" as the right one. "But the execution of the idea was poorly handled and we all need to take some responsibility for that, including myself."
Asked if the Cabinet had been told about what the potential level of job losses would be on schools and technology centres he said: "No, not to that level of detail, no."
But he had believed that between the Budget and September 1 when teacher entitlements for 2013 were finalised, it would be possible to work on a transition with the 10 per cent of schools that had been due to lose more than one teacher. That turned out to be wrong.
The Government left a "void" that was filled by opponents to the policy.
Educational Institute president Ian Leckie said the education sector leadership group had requested tomorrow's meeting with Ms Parata to follow up last week's decision on class sizes.
The group would meet first.
Some members of the group last week said they had been willing to sit down and discuss where savings could be made in education but Mr Leckie himself was not keen.
"It's not our budget. If we were given the budget we would love to discuss where and how that budget was shaped. Is it our responsibility to find the $40 million needed out of the Government's $10 billion [education] budget?" he asked. "Which part of education don't we like?"
Ms Parata said the Government remained focused on raising achievement for all through quality teaching.
She wanted the first meeting of the cross-sector forum to be held by the end of the month and said terms of reference that aligned with the Government's plan for education would be finalised at that time.