The percentage of high-schoolers in the U.S. who are getting their diplomas has reached record levels, and the student populations that have traditionally lagged behind—particularly poor children of color—account for much of that progress.

The latest figures, contained in a report published this week, suggest that the country is on track to reach a high-school graduation rate of 90 percent by 2020—a goal set by the coalition of organizations that produced the analysis and has tracked data from the National Center for Education Statistics annually over the past decade or so. In 2013, the most recent year for which comprehensive is available, 81 percent of the year’s class members graduated. (The report generally calculates rates by dividing the number of students who graduate in four years and receive a regular high-school diploma by the total number of students in the graduating class’s cohort; this is the metric used here whenever graduation rates are referenced.)

Boosting graduation rates has become a priority for districts across the country, in large part because of the ever-increasing importance of a high-school—and postsecondary—degree in the U.S. economy. Many of the 2015 report’s findings are certainly encouraging: Most states hit or exceeded the national average, including a few that are already very close to reaching that 2020 goal. Students of color are making the biggest gains, with Latinos, the fastest-growing student population, at the forefront of that trend. The number of “dropout factories”—high schools whose 12th-grade classes are drastically smaller than their ninth-grade ones—has also gone down.

But those are nationwide results. Outcomes varied greatly from state to state, which according to the report suggests that any gains were possible thanks to local education-reform programs, not necessarily because of broad socioeconomic trends. The graduation rate for low-income kids, a growing demographic nationally, was 15 percent lower than that for their more affluent peers. Meanwhile, the progress that was made among disadvantaged students was hardly universal. More than a dozen states still fell below the national average, and a handful of those states—including Arizona, Illinois, and New York—even saw their graduation rates drop.

Graduation Rate Change From 2010-11 to 2012-13, by State

The six states whose rates dropped (from biggest to smallest percent change): Wyoming, Arizona, Illinois, Vermont, South Dakota, and New York. (GradNation / NCES)

Arizona, Illinois, and New York are among the states identified in the report as particularly “worrisome,” in part because their income-based graduation-rate gaps widened, too. Socioeconomic characteristics often overlap in America, a dynamic that’s particularly true in these states, which are each home to some of the highest enrollments of low-income children of color. “Minority students will track really closely with low-income [trends], and that’s a really difficult thing to pull apart,” said Erin Ingram, one of the report’s researchers and an advisor at Civic Enterprises, an education policy and strategy firm.

U.S. High-School Graduation Rates Over Time

The orange line represents the “Adjusted Cohort Graduation Rate,” the metric used by the federal government since the 2010-11 school year and cited throughout this analysis. The blue line represents the “Average Freshman Graduation Rate,” a metric commonly used in the past that is less accurate but useful for analyzing longitudinal data. (GradNation / NCES)

A closer look at the data suggests that there can be an inverse relationship between the number of minority children enrolled in a state and the achievement levels of those children. Of the six states that collectively account for 70 percent of the country’s Latino students, only half of them graduated Latinos at rates above the national average for that demographic. Arizona, which has one of the highest percentages of Latino students, experienced the second-sharpest decline in overall graduation numbers, with just three-fourths of the 2013 class graduating; New York and Illinois have comparable findings. Seven states with either consistently low graduation rates or recent declines, including New York and Illinois, collectively educate more than four in 10 of the country’s African American students.

Though the exact reasons behind these nuances are complex and tricky to delineate, what the findings do reveal is that large concentrations of disadvantaged students might not be favorable for those kids’ academic success. In a way, this dynamic is hardly surprising given the correlation between race and poverty, as well as the years of well-established research showing that socioeconomic isolation handicaps student learning. As the sociologist James Coleman concluded in his 1966 “Equality in Educational Opportunity” report, concentrated poverty in schools undermines the academic achievement of poor and minority children. Unfortunately, concentrations of poverty have become more severe over the years: In 2000, one in eight schools was characterized as high-poverty; by 2011, the ratio had grown to one in five.

Why large swathes of students are struggling to graduate in New York and Illinois might have to do with the increasing concentration of poverty in urban areas. (Between 2000 and Great Recession, the number of people living in “distressed neighborhoods”—in which at least 40 percent of residents live below the poverty level—grew by 5 million, according to a Brookings analysis of census data.) On average, roughly two-thirds of students in the country’s largest 10 school districts are low-income, compared with about half of the students nationwide. New York City, which is by far the nation’s largest school district, was 67 percent low-income during the 2012-13 school year, and an almost equivalent percentage of kids in the public-school system identified as black or Latino. And in Chicago, which is the country’s third-largest school district, 85 percent of kids were low-income that year. The percentage of black or Latino students in Chicago was identical to its low-income statistics, too.

The structure of the New York City and Chicago school systems is also noteworthy: Both districts are relatively unusual in that the school a student attends isn’t necessarily based on where he or she lives. The two cities each have have a number of prestigious, highly selective public schools that admit students based on their academic merit. In New York City, eight public high schools admit students based exclusively on how they score on a rigorous standardized test. This system has come under scrutiny in recent years because the schools admit very few black and Latino students—a policy that critics say contributes to the vicious cycle of race- and class-based inequality in the city. The NAACP’s legal arm for its part filed a complaint with the U.S. Department of Education in 2012 that said the school district’s “exclusive, unjustified, and singular reliance” on the admissions exam means that “many fully qualified, high-potential students are denied access to the life-changing experiences that the Specialized High Schools offer.” The complaint is still pending.

Ultimately, what happens in large districts such as these, according to the report, has significant impact on the state numbers. “Some of these really big districts that are struggling are causing ... states to fall backwards in terms of their minority [graduation] rates,” Ingram said. “It could be they’re having a hard time dealing with concentrated poverty; it could be that for some of these places they had a really huge influx of English language learners, and that’s something thats new for them ... It could be a bunch of things.”

The same challenges could be true for Arizona, Ingram said. But unlike New York and Illinois, Arizona experienced declines in all of its major districts, including two (Mesa and Tuscon) that are among the country’s largest. The report cites the extremely high percentage of Latino students as a key reason behind the poor outcomes in Arizona—a state whose policymakers have a reputation for harboring anti-Latino sentiments, partially because of policies directly aimed at schools. “Arizona must carefully consider how to regain the ground it has lost in order to raise graduation rates for this subgroup, and in turn, its graduation rate for all students,” the report says. The table below shows the states that either had notably low Latino graduation rates in 2013 or, like Arizona, experienced declines in the rates for that demographic.

States With the Worst Graduation Outcomes for Hispanic/Latino Students, 2012-13

Nationally, the average graduation rate for Hispanic/Latino students in the 2012-13 year was 75 percent, up from 71 percent in 2011. (GradNation / NCES)

This table lists the states with the highest concentrations of Latino students (Arizona, Illinois, and New York are on both this table and the one above).

States With Largest Hispanic/Latino High-School Enrollments, 2012-13

Of the six states with the highest numbers of Latino students, only three have graduation rates above the group’s national average of 75 percent. (GradNation / NCES)

Poverty and race can hinder academic opportunity in myriad ways. And the cognitive, emotional, and nutritional disadvantages of growing up poor—realities that can significantly reduce a child’s chance at success later in life—are often exacerbated by school-funding inequalities. Districts serving high-poverty populations tend to receive less monetary support than do their wealthier counterparts, a phenomenon that’s particularly true in states that rely on property-tax revenue to fund schools. In a country plagued by growing inequality, it’s hardly surprising that a student’s economic background can predict the likelihood that the student will get a diploma.

Moreover, schools with large populations of these disadvantaged students tend to offer fewer challenging courses, including those that are key to preparing kids for college. A fourth of the high schools in the U.S. with the highest percentages of black and Latino students, for example, don’t offer Algebra II, while a third don’t offer chemistry. And when a school does offer AP classes and other challenging programs, minority students are often placed on low-level tracks—even if they demonstrate the proficiency to take those challenging courses. A recent College Board study found that a majority of the black and Latino students who fulfilled testing benchmarks that would’ve qualified them to take AP math didn’t participate in the program.

“They have lower expectations, they get lost in these urban districts, and then—because they’re never identified and pushed to try more challenging courses—they have less interest in school, get bored, get distracted, drop out,” Ingram said hypothetically. “That could be part of the reason.”

Another factor cited in the report is the growing prevalence of zero-tolerance discipline policies, which tend to fall disproportionately on minority students compared to their white peers. Research shows strong correlations between exposure to school discipline and dropping out, with one study suggesting that kids who were suspended even once in the ninth grade are two times as likely to drop out. A number of large, urban school districts, have started to prohibit these practices, however, including Los Angeles Unified and, just this year, New York City.

Whether New York City’s new policy will have a positive impact on its graduation numbers is still unclear. But in the two years since Los Angeles implemented its change, graduation rates have—at least according to district reports—gone up by 12 percent.