A study released by the U.S. Education Department reports that more than half of America’s high school seniors do not have even the most basic grasp of U.S. history, showing no improvement in a nationwide test since 1994. The results are virtually unchanged after seven years of concerted effort to bolster history instruction. The results are based on the NAEP exams, which educators view as one of the best measures of U.S. student achievement. The NAEP exams are considered challenging and are taken by a national sample of students.