WASHINGTON (AP) – The record high American graduation rate masks large gaps among low income students and those with disabilities compared to their peers.

There are also wide disparities among states in how well they are tackling the issue.

“This year, we need to sound a stronger alarm,” said Gen. Colin Powell and his wife, Alma Powell, in a letter released Tuesday as part of an annual Grad Nation report produced in part by their America’s Promise Alliance organization. The report is based on 2013 rates using federal data, the most recent available.

The nation’s overall graduation rate has reached 81 percent, a figure frequently touted by Education Secretary Arne Duncan. Duncan said Tuesday in a statement that the gains are encouraging, but “we know that more hard work remains to truly prepare all – not just some – students for success in college.”

Here are five things to know about high school graduation rates:

THE GOOD NEWS:

More students are graduating from high school than ever before, with large gains among African-American and Hispanic students. Since 2006, the percentage of black students graduating has risen 9 percentage points to 71 percent and Hispanic students has risen 15 percentage points to 75 percent.

The improvement is due to a variety of factors, including greater consistency in comparing graduation rates from state to state and the development of systems to identify and target at-risk students. The increase in the graduation rate also has been accompanied by a decline in the number of “dropout factory” schools, where 60 percent or less of students graduate.

The report estimates that the U.S. is on track for a 90 percent high school graduation rate by 2020.

STATE-BY-STATE COMPARISONS:

Graduation rates among the states vary, ranging from 90 percent in Iowa to 69 percent in Oregon.

Gains have been fueled, in part, by large growth in some of the nation’s largest states, including California, Florida, Georgia, and North Carolina. But 15 percent of the nation’s high school students attend school in New York, Illinois, Washington and Arizona, where rates are declining or stagnating.

STUDENTS WITH DISABILITIES:

Students with disabilities graduate at a rate of 62 percent, 20 points behind the national average. The rate is 2.9 percentage points higher than two years earlier.

These students include those with intellectual disabilities with significant limitations, but also a wide range of other disabilities such as autism and speech impairments.

It’s estimated that 85 percent of students with disabilities can do grade-level work, said Katy Neas, executive vice president for public affairs at Easter Seals. Neas said there have been improvements in the number of students with disabilities earning standard diplomas, but historically low expectations kept these students from getting the support they need.

“When these kids get the right services and support, they can be successful in grade level academic work,” Neas said.

LOW-INCOME STUDENTS:

The graduation rate for low-income students was 73 percent. It’s moved up 3 points in the last two years, but is still 8 percentage points below the national overall rate.

In Kentucky and Texas, 85 percent of low-income students get a diploma. In contrast, 65 percent or less of low-income students do in Alaska, Oregon, Colorado, Minnesota, Georgia, Michigan, Nevada, Wyoming, New Mexico or Washington.

In Kentucky, where there’s about a 1 percentage-point difference between the graduation rate of low-income students and the overall population, Dale Winkler, a state education official, said there’s been a years-long effort to tackle the problem. The efforts include districts and later the state raising the compulsory attendance age to 18, changing the state’s standards and assessments system, required interventions for students off track, and incentivized early graduation, Winkler said.

“It’s a lot of work,” Winkler said, adding that districts have school leaders who have been engaged in helping to make improvements.

MINORITY STUDENTS:

Six states combined to educate more than 70 percent of Hispanic or Latino students, but Texas is the only one that has a graduation rate for these students above the national average of 81 percent.

Michigan, New York, Ohio, Georgia, Florida, California and Illinois are collectively home to more than 40 percent of African American students. These states graduate only about 6 out of 10 black students or have recently had declines.

“Minority students continue to face barriers in their academic success, including discipline disparities that push them off track for graduation, language barriers and lack of access to rigorous coursework that will enable them to be successful in college and career,” the report said.