Schools Chancellor Joel Klein and his principal, Mayor Bloomberg, set sail this morning in search of a productive future for all the children of New York City.

It is the final leg of a grand voyage of discovery, and it’s going to be a difficult, politically dangerous journey.

But they hold the moral high ground.

They have few friends in the public-school establishment; but they deserve, they have earned, and they must have, the good will of the people of New York City.

They get the benefit of every doubt encountered along the way.

All disputes must be resolved in their favor.

For purposes of the debate that begins in earnest this week, they are presumptively correct.

On everything. Until proven otherwise.

As Klein and Bloomberg proceed, the other side – the unions, the self-appointed advocates, the bought-and-paid-for politicians both here in the city and up in Albany – will have prescriptions of their own.

But they have no moral standing in this discussion.

They’ve had their chance.

They, in fact, are the failed system that Klein and Bloomberg have undertaken to reform.

And it simply is not in that system’s interests that the New York City public schools substantively change at all – let alone for the better.

The city has spent more than $100 billion on its schools over the past decade, to no discernible good effect.

So much money.

So little literacy.

But the teachers got paid, and well; so did their unions; so did the advocates, with their political agendas and fat, tax-fed consultancies – and so did the politicians.

Finally, with the public choking on failure, it seemed that change had become possible.

The unions fought it.

So did the politicians – especially in the state Assembly.

But it happened anyway.

So, despite two years of special-interest obstructionism, the schools open this week under the theoretical control of Mayor Bloomberg.

Change is good.

But it is not necessarily reform.

Whether the mayor has actual control of the schools remains to be seen.

To say nothing of effective control.

For as much as was spent on the public schools in the past 10 years, half-again as much will be spent over the next 10 – $150 billion, probably more.

This is serious money, even in New York.

It is not a bounty willingly to be surrendered to the control of a fellow like Joel Klein – who humbled Bill Gates and Microsoft for the Clinton Justice Department.

He’s nobody’s fool, for sure.

But is he tough enough to crack the United Federation of Teachers and its poodles, Assembly Speaker Sheldon Silver and his public-school go-fer, Assemblyman Steven Sanders?

Not by himself, it’s safe to say.

So, is Bloomberg up to the challenge?

There is very little in the public record suggesting that the mayor has the stomach for the fight he has picked.

The unions and the special interests undressed him two years running on budgetary and related matters.

He publically declaims his inability to move Albany on New York City’s other multibillion-dollar, special-interest-driven budget-buster, Medicaid.

Privately, say some who have heard him, he simply is pathetic on the subject.

Thus, on the matter of mayoral chops, there is cause for concern.

Then again, Bloomberg wasn’t elected on a promise to mend Medicaid.

He was hired to fix the schools – or at least to set the process credibly in motion; maybe he’s been holding his heavy artillery in reserve for the battle that begins this morning, when teachers report for orientation and instruction.

His mayoralty will be judged on the outcome of this effort – a matter of scant import judged against the lives of the kids who should be, but who so rarely are, the true focus of concern.

New York City’s stake in a happy outcome is manifest.

So, power to Mike and Joel – intrepidly entering a mare incognito where truly there be monsters.