At their core, public charter schools are about one simple trade-off: a charter school receives more autonomy to operate in the way its staff thinks will provide the best results for students.

In return, it accepts greater accountability for the results it achieves academically and operationally -- with the understanding that if a school fails, it will be closed. That is why charters get a license to operate for five years at a time — and have to make the case that they should be renewed.

Because accountability and autonomy are what charters are about, the decisions this week to close one poorly performing charter school, only conditionally renew another and provide notice to three others that they will be closed shortly unless they clean up their acts, is exactly the right move to ensure charters fulfill their promise to students and their role in the larger public education system.

The decisions also show not just what chartering is at its heart, but also how complex, and even difficult, chartering actually is.

Take, for instance, the decision to not renew the charter of an elementary school in Far Rockaway, Queens, an isolated area that has few good choices for its parents.

The school, Peninsula Prep Academy Charter School, has its good points: 60 percent of its students are proficient in math; its performance is more or less on par with surrounding district schools. And last year its proficiency rates increased.

Moreover, it has a thoughtful and caring leadership team that works very hard. Doesn’t that make a case for a school that should continue to operate?

Perhaps, but when one looks at the school’s scores in reading (the most important subject of all), less than half of its students are proficient, even in fifth grade. Those children are unlikely to succeed in middle school or to flourish later in life. That’s a tragedy and unacceptable.

Moreover, the recent increases from a very low level do not mean that the school’s upward trajectory will continue; based on past experience, this more likely marks the upper limits of the school’s performance.

But even more fundamentally, after having seven years to get it right, the school didn’t meet the promises it made when it opened, which was to have at least three-quarters of its children at proficient levels in both math and reading.

Bottom line: If the city’s Department of Education were to renew the school, it would be saying that it is enough for a school to be no worse than surrounding schools or to succeed with less than half its students.

If that is the standard for charter schools, then it is not clear why we need them in the first place or why we would think that charter schools would be able to spur improvements in traditional public schools. Far from being exemplars, they would simply become just another group of mediocre institutions.

The city's Education Department, as well as a second charter authority, the State Education Department, were also faced with three high schools -- all part of the Believe Charter Network in Brooklyn -- that are performing reasonably well academically, but are mired in allegations of financial improprieties with seemingly no oversight from their board of trustees.

Currently, the schools are under investigation by the attorney general. They’ve been given 30 days to enact a sweeping remedial action plan or be closed at the end of the year.

If the schools close, more than a thousand students will have to find new high schools -- a particularly hard thing for the juniors who have a single year left.

Under these circumstances, a lot of people will reasonably ask, why close the schools? If they’re performing well, and the issues are at the level of the schools’ leadership, why not replace the management and let the schools continue? Why should students and parents suffer when adults don’t do their job? That sounds reasonable but is actually very problematic.

First, chartering doesn’t give authorizers the right to remove principals or board members and replace them with their hand-picked successors.

Instead, authorizers have three options: renew schools, not renew them, and in extreme cases shut them down.

What they can’t do is micromanage a school’s affairs, and for good reason. If authorizers could directly manage all charter schools, then the autonomy charters are given, and the reason they exist, would be snuffed out.

Second, the fact is that even if authorizers had the power to declare who goes or who stays, there is not a long line of competent leaders and board members who would be willing to govern a school that is under the shadow of an investigation by the attorney general. We also have few if any organizations willing or capable of taking over troubled schools.

These factors have several important implications: authorizers should have a rigorous approval process at the beginning of the chartering process so that we authorize more high-capacity schools.

There should also be contingency plans in place in case a school fails to give students seats at better existing schools.

And as always, the city must create new schools in these neighborhoods (district and charter) that desperately need them.

These decisions show what is good about chartering. It creates clear, bright lines of accountability and gives autonomy to great leaders and teachers to build a school that succeeds for students. But it also demonstrates that schools will close and parents and students may be left with no good choices.

It isn’t a perfect way to do things -- there isn’t one. But it is one important tool that we have in seeking to arrive at a day when every school is succeeding.