For Louisiana’s long-suffering public schools, it often seems as though the goalposts are not just being moved but being rebuilt in all shapes and sizes.

Schools have been under pressure to lift test scores and reduce dropout rates since the federal No Child Left Behind Act went into effect more than a decade ago. School performance scores are supposed to communicate to parents and policymakers whether schools are improving over time. Yet hardly a year goes by without changes in how those scores are calculated in the first place.

Indeed, the scores released by state officials last week came with all kinds of changes in methodology.

The state tweaked how it hands out so-called progress points for making gains with students who have fallen behind. It stopped averaging two years’ worth of data, which it used to do in order to limit volatility. And it used a curve in assigning schools the letter grades — A, B, C and so on — that correspond with performance scores, hoping to avoid big declines during the transition to a new set of academic standards.

“It’s a constantly evolving gumbo recipe,” said Ramsey Green, a former state official who now chairs the board of the New Beginnings Schools Foundation, a New Orleans charter school group.

Not that Green objects to any of these changes. He doesn’t. Taken individually, every alteration in how performance scores and letter grades function comes with a clear enough rationale, sometimes controversial but usually vetted by the state board of education.

It is the cumulative effect of these changes that underscores the tension involved in grading schools — the need for a steady bar to indicate progress over a number of years but also the flexibility to refine and raise the state’s standards.

State Education Superintendent John White argues that Louisiana is striking the right balance. Performance scores, he acknowledges, continue to shift from one year to the next in order to reflect changing priorities. But the raw test scores that go into them remain a steady gauge going back to the late 1990s.

Performance scores, for instance, used to be assigned on a 200-point scale and factor in attendance rates in the elementary grades, along with scores on the state’s LEAP exams. Now, it’s a 150-point scale and attendance doesn’t count at all.

Look only at the LEAP results, on the other hand, and things are more constant. The tests are adjusted to be equally difficult every year, even as the questions change. So the proportion of students scoring at “basic” or “mastery” offers a more-or-less unchanging benchmark.

“The tests’ job is to measure with consistency,” White said. “The accountability system is supposed to reflect our changing expectations. It’s a natural thing that your expectations should change over time.”

And change they have, especially for high schools.

At the secondary level, there is not really even a constant way of measuring test results. The state has abandoned the catch-all Graduation Exit Exam in favor of end-of-course exams for each subject. ACT results remain constant going further back, but they have factored into performance scores only since 2013, so not every student was required to take that test until recently.

Again, there is a logic to the shifting standards. State officials want schools to prove they are getting students ready for college, so why not use the same test that many colleges themselves use for admissions?

A similar rationale underlies changes in how the state calculates progress points. Beginning in 2013, a school could boost its performance score by making greater-than-expected progress with students who scored below basic on the LEAP exam the prior year.

Initially, schools would get credit only for students who made that progress but still landed below basic. White said schools complained that it made no sense to essentially penalize them for clearing that bar, so the state dropped the stipulation this year, which resulted in more schools earning points.

There is a risk to making constant adjustments. The political struggle over education in Louisiana, as elsewhere, is fierce. And every tweak in the accountability system brings renewed accusations that state officials are rigging things in favor of their favored reform ideas, like the independent charter schools that now educate most students in New Orleans.

“The scores, as far as we’re concerned, are noise now,” said Steve Monaghan, head of the Louisiana Federation of Teachers. “There is always going to be the suspicion that this is being handled in a way that advantages one and disadvantages another.”

Nevertheless, Louisiana is getting ready for yet another radical overhaul of its standards, beginning in 2016.

As in prior years, the tests themselves will be no more difficult. Scoring at basic, or level 3 on a 5-point scale, will be just as tough as it is today. But the state has decided that level 3 isn’t good enough anymore.

Gradually, any given school will have to get more and more of its students scoring at level 4, or “mastery,” in order to earn points in the accountability system.

That’s part of the transition to the controversial new Common Core standards, which are intended to spell out what a student should learn in each grade and provide a common measuring stick across all of the more than 40 states that are adopting them.

Getting all students, or at least a solid majority of them, to mastery will be a big lift, even considering that schools have until 2025 to fully adjust.

This year, for example, about 56 percent of New Orleans eighth-graders in the Recovery School District, the state’s turnaround agency for struggling schools, scored at basic or better on English exams; only 13 percent scored at mastery or better.