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Each year, when they get to campus, more than half a million American college students have to take so-called remedial or developmental education classes to teach them basic math and English skills they should have learned in high school. And that’s not even the full story. The full story cannot be accurately told, because of problems in how states collect the data — if they collect it at all.

Here’s what we do know:

During the 2014 academic year, at least 569,751 students at 884 public two- and four-year colleges across 33 states were deemed not ready for some college-level work.

The national total is likely significantly higher, however, due to inconsistencies in how the data was collected. In fact, there’s no way to know exactly how many students are placed in these courses, even though they are a financial drain on students and taxpayers and a huge stumbling block on the way to a degree.

The Hechinger Report spent months collecting remediation rates from public institutions across the country, and learned that the data is tracked differently from state to state, making national comparisons difficult.

“If you have nothing or little data or it’s inconsistent … how are we going to gauge whether we’re making progress?”

Some states report information for all students, for instance, while others report information only for incoming recent high school graduates. Some report it for the fall semester only, while others include data from the entire academic year. Some states provided data only for their two-year schools; some just for their four-year schools. Some states hadn’t collected data since 2012, and some states didn’t have any remediation data available to share.

Related: Most colleges enroll many students who aren’t prepared for higher education

Even in the many states that do track this data consistently, different schools may use different cutoff scores on remedial course placement tests.

And the criteria can change at any time, as many colleges and universities try to revamp remediation classes as a way to graduate more students more efficiently. At the same time, K-12 education systems across the country are focusing more than ever on producing “college-ready” students.

But without better data, it’s hard to tell whether any of this is working.

“If you have nothing or little data or it’s inconsistent … how are we going to gauge whether we’re making progress?” said Mary Fulton, a senior policy analyst at the Education Commission of the States.

In 2014, she co-authored “A Cure for Remedial Reporting Chaos,” which revealed that only 32 states reported annual statewide remedial education information and, of those, just 15 states reported remediation rates back to high schools and 13 followed remediation students to see how they did in college.

“There was no consistency in whether states reported at all, or on a regular basis and what was included in those reports,” she said. “It’s just a lot messier than we ever anticipated.”

One nonprofit organization, Complete College America, has made a push to solve this problem by getting states to agree to track not only remediation students’ enrollment rates, but also course completion and graduation rates for those students. Its 2012 report “Bridge to Nowhere” found that across 33 states 52 percent of entering students at two-year schools and 20 percent at four-year schools were placed in remedial classes in the fall of 2006.

569,783 students at 884 public two- and four-year higher education campuses across 33 states were deemed not ready for some college-level work.

Despite the progress that organization has made, Hechinger’s investigation met with multiple obstacles to getting recent data broken down by campus. Three states — Arizona, Nebraska and New Hampshire — specifically told us they didn’t collect these numbers from their state institutions. Pennsylvania did not respond to repeated requests, while Wyoming was in the process of redoing its own analysis of the information for its technical colleges and unable to provide it publicly.

The South Dakota university system had numbers to share, but the state’s technical institutes only tracked the number of underprepared students who eventually graduated, not the number who enrolled in remedial courses in the first place. Missouri declined to give a breakdown of its remediation rates by campus, citing potential errors. Instead, it broke its data into sectors, such as “moderately selective” and “open two-year.”

Similarly, Ohio only publishes statewide figures and declined to fulfill a public records request for campus-level data, explaining that, by law, it is not obligated to create data that doesn’t already exist. Both the Iowa university system and New York State would not provide the data without  a  public records request. Two of Iowa’s three universities required payment for it — $30 for Iowa State and $150 for the University of Iowa. (The University of Northern Iowa and New York State completed the request for no charge.)

The problem with delayed, messy or missing remediation data isn’t just about a state’s ability to track remediation at its colleges, said Regina Deil-Amen, a professor of higher education and sociology at the University of Arizona. The problem affects high school reform as well.

Related: Remedial classes are a huge stumbling block on the way to a degree. That’s why this community college doesn’t have them

Over the last six years, every state has updated its K-12 standards, with the majority adopting the Common Core, which maps out what students need to know and be able to do in each grade in math and English in order to be ”college and career ready.”

The standards are “supposed to be about making students competent for college-level work,” Deil-Amen said. “When you have no way of seeing how their competency pans out, it’s problematic.”

As the Education Commission of the States 2014 report pointed out, while several states regularly produce reports that tie higher education remediation rates back to specific high schools, most states do not. So, college-readiness is usually judged by students’ pass rates on standardized tests taken in the 11th grade.

This disconnect between the K-12 and higher education systems has long been an issue, according to José Luis Santos, vice president of higher education policy and practice at the Education Trust. If more states collected better data about students needing remedial classes in college, that would be a starting point. The next step, though, would be to make sure that high schools learn about the findings.

“The data points are hugely important,” he said. “But it’s not until people sit down together across these systems to look at where there are failings … if they sat together and looked at that high need of remediation, there could be some true partnerships there.”

This story was produced by The Hechinger Report, a nonprofit, independent news organization focused on inequality and innovation in education. Read more about higher education.

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