High school seniors' scores on a national history assessment remained flat between 2006 and 2010, according to a report released Tuesday by the National Center for Education Statistics (NCES), a government organization.

The National Assessment of Educational Progress (NAEP) tests public and private school students in grades 4, 8, and 12 in mathematics, reading, science, writing, the arts, civics, economics, geography, and U.S. history. The history test was given in 1994, 2001, and 2006. History scores were lower than any other subject, though NCES Commissioner Jack Buckley cautioned against comparing tests.

"Trying to compare proficiency across subjects is problematic," he said during a conference call with reporters. "Tests are done independently across all subjects. While if you line them all up, history looks lower, it's not a fair comparison."

NCES divides the 500-point scale into three passing benchmarks—"basic," "proficient," and "advanced." Just 45 percent of 12th graders scored at or above "basic" on the history test. About 10 percent of seniors scored "proficient," and 1 percent are considered to have an "advanced" knowledge of U.S. history. A student is considered to have a "basic" knowledge of U.S. history if he or she scores at least a 294 on the 500-point scale. In 2010, the average score for seniors was 288, which was a slight improvement from 1994 scores, but not significantly different from scores in 2001 or 2006....