The latest results on the most important nationwide math test show that student achievement grew faster during the years before the Bush-era No Child Left Behind law, when states were dominant in education policy, than over the years since, when the federal law has become a powerful force in classrooms. Scores increased only marginally for eighth graders and not at all for fourth graders, continuing a sluggish six-year trend of slowing achievement growth since passage of the law, which requires schools to bring 100 percent of students to reading and math proficiency by 2014. On the most recent test, 39 percent of fourth graders and 34 percent of eighth graders scored at or above the proficient level. 'The trend is flat; it's a plateau. Scores are not going anywhere, at least nowhere important,' said Chester E. Finn Jr., president of the Thomas B. Fordham Institute, a research organization in Washington. 'That means that eight years after enactment of No Child Left Behind, the problems it set out to solve are not being solved, and now we're five years from the deadline and we're still far, far from the goal.' The test, known as the National Assessment of Educational Progress, was given to 329,000 fourth- and eighth-grade students. Results in reading are to be released next year, officials said. 'This is the first time in 19 years that fourth-grade math scores are flat,' said Education Secretary Arne Duncan. 'We've got to get better faster.' The latest scores were especially disappointing because score gaps between white and minority students did not diminish at all since the last time the math test was administered, in 2007. On average, the nation's fourth graders scored 240 on a 500-point scale, just as they did in 2007. White fourth graders, on average, scored 248, Hispanics scored 227 and blacks scored 222. Eighth graders, on average, scored 283 on the same scale, up from 281 in 2007. White eighth graders, on average, scored 293, while Hispanics scored 266 and black eighth graders scored 261. The gap of 32 points separating average black and white eighth graders represents about three years' worth of math learning. Enactment of the No Child Left Behind law in 2001 followed a decade dominated by a standards and accountability movement that brought deep changes to public schools. Educators and policy makers, in nearly every state, laid out standards as to what students were expected to know in each grade and subject, and required schools to use those standards to guide instruction. They also established standardized testing regimes intended to measure whether students were meeting the standards and to hold schools accountable for student achievement. The federal law, proposed by President George W. Bush and passed by bipartisan majorities in Congress in his first year in office, sought to build on the standards movement with many new federal rules, including a requirement that states administer reading and math tests every year to students in grades three through eight and once in high school. It required schools to publish their scores on state tests not just as averages, but broken down by students' race, sex and other groups, a rule that most educators agree has focused attention on narrowing achievement gaps. And it raised the importance of the National Assessment, requiring the Department of Education to increase the frequency of its administration in math and reading to once every two years, to help Americans monitor progress toward the goals of universal proficiency and the elimination of the achievement gap. The latest results on the National Assessment show that in the six years since the law took effect, fourth-grade scores have risen by five points, to 240 from 235. That is slower growth than during the seven years preceding the federal law, when average fourth-grade math scores grew by 11 points, to 235 in 2003 from 224 in 1996. 'Either the standards movement has played out, or the No Child law failed to build on its momentum,' said Mark Schneider, who from 2005 to 2008 was commissioner of the arm of the Department of Education that oversees the National Assessment. 'Whatever momentum we had, however, is gone.' No one can say for certain why achievement progress has slowed since the federal law took effect, and Mr. Schneider and other experts warned that economic, demographic and social factors other than the law itself may be to blame. But an unintended consequence of the law has been that many states have lowered the rigor of their standards and the difficulty of their tests to avoid sanctions the law imposes on failing schools, a process that Duncan has called a 'race to the bottom.' David P. Driscoll, chairman of National Assessment Governing Board, said at a news conference in Washington announcing the scores: 'Mathematics achievement is not close to where it should be.' 'A major reason,' he said, 'continues to be the lack of content knowledge and mathematics preparation of our teachers.' William Schmidt, an education professor at Michigan State University, also called the results disappointing. 'We're just inching upwards, and we've only got about a third of our students proficient,' Schmidt said. The large variation in average scores by state, he said, should be a focus of national analysis. In Massachusetts, for instance, where educators have sharply raised math scores in recent years by carefully reworking standards and instruction, 57 percent of fourth graders scored at or above proficient on the latest test. That compares with Mississippi, where only 16 percent of students scored at proficient. 'How can we as a nation allow such disparity?' Schmidt asked. 