A 2008 report offered a dire warning: U.S. schools were falling behind their international peers. Its prescription: states should “adopt a common core of internationally benchmarked standards in math and language arts.”

The idea of the Common Core would soon gain steam. Thanks to interest from state leaders and financial incentives offered by the federal government and private philanthropies, most states adopted new academic standards over the next few years. That would soon mean new tests, new textbooks, and new teaching methods — and in many places, backlash to those changes.

But amid the fierce debates, there has been virtually no research on whether the standards were actually accomplishing their goal of improving student learning.

Until now. A new study, released in April through a federally funded research center, shows that states that changed their standards most dramatically by adopting the Common Core didn’t outpace other states on federal NAEP exams. By 2017 — seven years after most states had adopted them — the standards appear to have led to modest declines in fourth-grade reading and eighth-grade math scores.

“It’s rather unexpected,” said researcher Mengli Song of the American Institutes for Research. “The magnitude of the negative effects tend to increase over time. That’s a little troubling.”

Studying the effects of Common Core is challenging, since the changes reached so many students nationwide at the same time — so there is a good deal of uncertainty in determining whether the standards were successful. And another study, which has not yet been published, offers a more encouraging view: the Common Core may have led to modest increases in test scores, though it only looked through 2013.

But the latest research suggests that even in the best case scenario, the academic shifts led only to modest gains for students, falling short of the far-reaching ambitions of Common Core advocates.

“It’s a good paper,” said John Young, a researcher with the pro-Common Core group Student Achievement Partners, speaking in his personal capacity about Song’s research. “But in some ways, maybe it’s a little too early to really know, because we’re still watching teachers change and improve.”

Tom Loveless, who has analyzed the standards for the Brookings Institution, says there’s a simpler explanation.

“One thing standards advocates need to think about is that this doesn’t appear to work very well,” he said.

New study is among the first to try to establish the effect of Common Core

How do you a study a policy as far-reaching as the Common Core, particularly one that was introduced alongside a host of other school reforms?

It’s not easy, but Song and her colleagues reasoned that some states were more affected by the switch to “college and career ready standards,” which meant Common Core in almost all cases. So they categorized states by the “rigor” of their previous standards and how similar those standards were to the Common Core.

They divided states into those more affected by the switch (because their prior standards were deemed less rigorous or less similar to the Common Core) and those less affected. Then they compared how each group’s scores changed on fourth and eighth grade NAEP tests between 2010 and 2017.

Common Core didn’t seem to help students’ scores, and over time the standards may have had an increasingly negative effect, according to the study, which has not been formally peer-reviewed.

Other researchers consulted by Chalkbeat, including Laura Hamilton of the RAND Corporation, say the study’s approach is a credible one.

“I’m not ready to conclude that the adoption of rigorous content standards is bad for student learning,” said Hamilton. “But I don’t look at this and think this looks totally wrong. It definitely looks plausible.”

Still, the approach has limitations. Most important is that the study is comparing two groups of states that adopted the standards — so if Common Core universally helped or hurt the states that adopted it, this study would miss that effect.

Another Common Core study points to more encouraging results, though it hasn’t yet been released

Joshua Bleiberg, a doctoral student at Vanderbilt University, is also studying the impact of Common Core on NAEP scores. His study starts examining student scores when new standards hit classrooms, not when states decided to formally adopt the Common Core. He also excluded states that ultimately dropped the standards.

That all seems to lead to different results. In preliminary findings shared with Chalkbeat, Bleiberg finds that the Common Core had small positive effects on NAEP scores through 2013. His study has not been released publicly, so it can’t be fully examined.

“This is not going to be the type of thing that is going to turn around the whole ship really quickly,” Bleiberg said of the standards. “I would think about [the effects] as quite small.”

There’s very little other research on the Common Core. A 2015 Kentucky study showed students who were exposed to the standards made larger gains than students who weren’t.

Morgan Polikoff — a professor at the University of Southern California and co-director of the center that released Song’s study — said the challenges in studying whether the Common Core worked are steep.

“I think that this question is more or less impossible to answer,” he said.

If Common Core failed, why?

By virtually all accounts, the introduction of the Common Core didn’t go as planned.

In New York City, for instance, teachers didn’t get textbooks aligned to the new standards on time. In Massachusetts, teachers said their training was simply low quality. Across the country, teachers said that implementing a new set of standards and state tests at the same time as new high-stakes teacher evaluation systems was untenable. These challenges are one obvious potential reason for the results of Song’s study.

“The statewide transition from old standards to new standards is really a massive undertaking,” said Song. “Maybe the new standards are well designed with good potential, but to realize this potential requires a lot more.”

The challenges may have been even steeper for states with standards that were very different than Common Core — the group the study zeroes in on — so it’s not entirely surprising their results are less positive.

“Maybe there’s chaos in the system,” said Young of Student Achievement Partners. “The negative results that they find is really just as much due to that happening.”

But the results are not getting better over time, according to Song’s research, so it’s hard to pin the findings on bad implementation.

That leaves Song puzzled. I don’t have a good hypothesis for why the effects actually grow over time,” she said. “That’s something I didn’t expect.”