SAN DIEGO — African-American elementary students in California were chronically truant at nearly four times the rate of all students during the last school year, according to a state report released Friday, that said poverty and suspensions were contributing factors.

The report by the California attorney general's office is the first time the data has been broken down according to race and income levels. Officials say such data is needed to address the problem.

It comes as new research from the U.S. Education Department's civil rights arm earlier this year has found racial disparities in American education, from access to high-level classes and experienced teachers to discipline, begin at the earliest grades.

Black students are more likely to be suspended from U.S. public schools — even as tiny preschoolers, according to the March report by the Education Department's civil rights arm.

The Obama administration has issued guidance encouraging schools to abandon what it described as overly zealous discipline policies that send students to court instead of the principal's office. And even before the announcement, school districts have been adjusting policies that disproportionately affect minority students. Overall, the data show that black students of all ages are suspended and expelled at a rate that's three times higher than that of white children. Even as boys receive more than two-thirds of suspensions, black girls are suspended at higher rates than girls of any other race or most boys.

The data doesn't explain why the disparities exist or why the students were suspended.

In California, the study found 37 percent of black elementary students sampled were truant, more than any other subgroup including homeless students, and about 15 percentage points higher than the rate for all students.

Overall, more than 250,000 elementary school students missed 10 percent or more of the 2013-2014 school year or roughly 18 or more school days. The absences were highest at the kindergarten and first-grade levels when children learn to read, according to experts.

Statewide, an estimated 73,000 black elementary students were truant last school year.

California law defines truancy as being absent or arriving more than 30 minutes late without a valid excuse three times in a school year. Students who miss 10 percent of the school year without good reason are considered to be chronically truant, which experts say increases their risk of failing.

Attorney General Kamala D. Harris has been pushing for the state to adopt a system that tracks the absentee rates of individual students. California is among only a handful of states that do not. Legislation for such a system is on the governor's desk.

The attorney general's office teamed up with a private company, Aeries Student Information System, which broke down the data from 32 school districts. The study found almost 90 percent of the elementary students who missed 36 days or more of the school year were from low-income homes.

"Because the state is not collecting this critical information, the attendance crisis among African-American children has largely remained hidden," the report states. "Therefore, we cannot conclusively explain the stark contrast between African-American elementary students' rates of absence and that of nearly every other subgroup. We do know, however, that African-American children experience many of the most common barriers to attendance — including health issues, poverty, transportation problems, homelessness, and trauma — in greater concentration than most other populations."

Research has found students who are truant starting at a young age are more likely to drop out. Dropouts cost the state more than $46 billion dollars each year, including more than $1 billion in juvenile crime costs alone.

Hedy Chang, director of Attendance Works, a nonprofit that studies chronic absenteeism, said students in impoverished areas often suffer from greater health problems, such as asthma, perhaps because the home is near a freeway. Their parents may be working and not there to see them off to school, she said. Crime may be deterring some from going out in their neighborhoods or they may be traumatized by what they've witnessed and act out at school, leading to them getting suspended instead of getting the help they need to stay in school, she said.

The state's largest school district, the Los Angeles Unified School District, has implemented changes after a civil rights investigation in 2011 found black students were underrepresented in gifted and talented programs but overrepresented in suspensions and disciplinary actions.

Truancy experts say school districts have seen success by providing one-on-one support.

Anna Salazar, who works with high-risk youth in the Los Angeles Unified School District, said she has found a child may be skipping school over something as simple as being embarrassed about having to wear dirty clothes.

"Once I build a relationship with them, I've found it's often something as simple and as tangible as that — needing a clean shirt," she said.