The gap in reading is especially dismal - only three states have managed to narrow the divide between black and white students in fourth grade, and no state has narrowed the gap in eighth grade.
There was more progress in math, at least among younger kids.
The findings constitute the first major Education Department report since President Barack Obama took office, though it was done by the agency's nonpartisan research arm, the Institute of Education Sciences. The report was based on test results from nationwide assessments from the early 1990s to 2007.
Racial disparity persists because black and white students alike are doing better, said IES associate commissioner Peggy Carr.
"Progress has been made on both accounts," Carr said. "It's kind of difficult to close the gaps when everyone is improving."
The report did not draw conclusions on the underlying reasons for the disparity, though it noted that poor children have lower scores and that a disproportionate share of minority students are poor. Researchers say the socio-economic gap is present even before children start school.
The achievement gap that separates minority and poor students from their white peers is viewed as one of the most pressing challenges in public education.
It was a central element of the 2002 No Child Left Behind law, which holds schools accountable for progress among every group of kids, including minorities, those who have disabilities and those who are learning English.
The law prods schools to improve test scores each year, so that every student can read and do math on grade level by the year 2014.
The report found that black students scored 26 to 31 points below white students, on a 500-point scale, in fourth- and eighth-grade reading and math.
It looked at the divide between black and white students in every state, finding:
Achievement gaps persist in every state for which data was available.
No state saw its achievement gap widen.
In math, the achievement gap narrowed in 15 states in fourth grade and in four states in eighth grade.