The only contentious change in schools during his first term was the national standards regime for primary schools, which faced plenty of outrage from the profession. But it was an issue teachers knew they couldn't win. How could national standards not be a good thing?
Teachers had to grit their teeth and accept the implication that they were not already working to reasonable standards. They had to agree the language they use in reports to parents is unutterably ridiculous and they couldn't say publicly that most parents couldn't handle the plain truth.
Hardest of all, they knew that measuring schools against national standards would allow newspapers to publish "league tables", creating winners and losers, and we couldn't have that. But we'd need a certificate in education to know why.
So the teachers seethed in their staffrooms and at their conferences. Their national unions, ever vigilant against market liberalism, could make little headway against Key and his first education minister, Anne Tolley.
Teachers had no respect for Tolley, she hadn't been one of them. She was just a parent who had taken a turn on a board of trustees. And she was so damned reasonable. Like Key she didn't seem to have an ideological bone in her body. Both just wanted more useful information for parents and for the Government.
They were so reasonable that Tolley agreed each school could set its own standards and the results would be issued in a form that wouldn't be a basis for league tables.
Still the teachers seethed, not all of them, of course, but the vast majority who vote Labour. They saw National re-elected and then - could you believe it? - Key gave Act a trial of charter schools. Charter schools are a direct challenge to the profession's control of education.
Not even the National Government of the 1990s had dared dabble in charter schools. It had run into enough trouble trying to "bulk fund" existing schools.
Charter schools, an American idea that has been taken up notably by black communities, would be given a slice of the taxpayers' education outlay to try something different.
The experiment has been put in the sensible hands of Act's Catherine Isaac and as yet it doesn't seem to scare anybody except teachers, for whom you would think it presents a rare opportunity.
I keep wondering what would happen if a government put up some public money for alternative newspapers. Journalists would be falling over themselves with ideas. Yet in the six months since the trial of charter schools was announced there has been no sign of an entrepreneurial spark in the profession.
Teachers have seen research from the United States that finds charter schools sometimes do better than public schools and sometimes worse. So there is a risk in innovation. There always is. The Government is willing to take it and the public doesn't seem to mind.
The public equanimity could be changed in much the same way that class sizes became an issue in recent weeks. The teacher union's most likely strategy would be to present charter schools as bulk-funding by the back door.
Teachers would be easily convinced that there is an agenda to set up two charter schools so that all others would have to be bulk-funded to compete with them.
There is nothing unusual about bulk funding. It is the way universities and medical practices and most other community services want to be financed. But it means that staff salaries and conditions are bargained directly with their employer and teachers don't want that.
Before you know it, they'd be facing performance pay and who knows what else.
When the Government saw the polls on class sizes this week it decided the savings were not worth the fight. It might soon regret that decision.
The polled questions were simplistic, the issue was not running deep. It would have dropped out of the news next week.
The Government's weakness will have teachers pumped.
