WASHINGTON (AP) — The national test considered the best measure of how high school seniors perform is suffering from plummeting student participation and growing questions about its reliability, according to a new report released Friday.

The National Assessment of Educational Progress, also known as the nation's report card, needs a significant makeover at the 12th-grade level, according to a commission created last year by the test's governing board to review the exam.

Among the biggest recommendations is expanding the test's basic purpose so that it gauges not just what 12th-graders know but also their readiness for work, college or the military. Such a change would require government approvals that could take years.

The commission also recommended that the test be required in every state in reading and math every two years, just as it is in those subjects in grades four and eight. That would produce the first-ever state results for high school seniors — not just a national average — to help policy-makers evaluate their school standards and make comparisons to other states.

"We need to know in America what 12th-graders know — it's important to the country — and we don't have a way presently to know that," said Mark Musick, the commission co-chairman and president of the Southern Regional Education Board.

The national test is given to a representative sample, not all students in a given grade, and that would not change under the commission's recommendations. The test would also remain voluntary and produce no individual scores, which critics say create student apathy.

The combined school and student participation rate in the 12th-grade test dropped to 55% in 2002, meaning almost half of those selected for the sample chose not to participate.

That response has put the test "right on the brink of not being able to say this information is reliable enough to use," Musick said.

Beyond mandatory state participation, the commission says the test leaders should come up with bold ways to get students to take the test and to encourage them to do well. Its ideas for incentives range from a written thank you from the U.S. president to the distribution of shopping "discount cards" to be used at bookstores and businesses that support the test.

"One of the challenges (the test) has had to contend with is getting parents and students to take it seriously, because no individual students get results," said Michael Nettles, commission co-chairman and senior research director at the Educational Testing Service.

"What this report suggests is maybe, if we can get the states to get more serious about it, along with the workplace and colleges, then parents and students will take a more serious look," he said.

Some of the proposed changes would require federal money and congressional approval.

The National Assessment Governing Board, which oversees the test, will begin reviewing the recommendations Friday and will seek comment from many groups over the next few months. The board is not expected to take votes on the ideas until August, said Charles Smith, the board's executive director and the former commissioner of education in Tennessee.

The report comes as the value of a high school diploma is facing increasing scrutiny, as colleges and employers complain of young people emerging from school with too few skills.

But it also comes as students face more tests than ever, said Bob Schaeffer, public education director at The National Center for Fair & Open Testing. He said expanding the size and intent of the test could raise its stakes and erode its credibility as a "neutral thermometer of American education quality."