San Francisco School Superintendent Arlene Ackerman rightly questions whether the graduates of the defunct Urban Pioneer Experiential Academy, a charter high school, "earned" their diplomas ("Superintendent challenges charter school diplomas," San Francisco Chronicle, Sept. 4).

She should apply her curiosity to all the district's schools, where thousands of students walk away with diplomas that signify little. Graduates in the city's high schools and across the state get diplomas merely for attendance. For those who bother to warm a seat, failure is not an option.

For many teens, the bogus diploma is the last step on a journey through school without any accountability. Social promotion, the practice of advancing students regardless of what they know, is the norm. The primary determinant as to whether a student earned a diploma must be what the student has learned.

Ackerman, for all her justified bewilderment and indignation, never once mentioned student achievement -- only credits. The two are not the same. Real learning, as opposed to credit earning, can be accurately measured only through tests.

The California high school "exit exam" will go a long way toward soothing Ackerman's doubts over whether students are "earning" their diplomas. This test is the capstone of the state's ambitious academic accountability plan. Students get multiple tries to pass the exam, which gauges their mastery of sixth- and seventh-grade math and Algebra 1, and English up to a tenth-grade level. The exam will also allow teachers, schools and districts to identify individual student weaknesses as well as wider problems, and it will be a beneficial diagnostic tool to evaluate teacher performance.

High schoolers statewide should have taken the exam next week, but California Superintendent of Public Instruction Jack O'Connell isn't giving them the chance. By axing tests for September and November, he's robbing confused administrators such as Ackerman of some bedrock to stand on when she evaluates her district.

The state superintendent is also robbing students of an exam that is for their benefit. For example, in its recently released independent evaluation of the exit exam mandated by the Legislature, the Human Resources Research Organization, an education consulting firm, found that because it is aligned according to specific standards, the exam served as an incentive for schools to implement the state's widely admired and rigorous academic content standards. The study found that 100 percent of the schools in the survey with high levels of standards coverage had pass rates of 75 percent or greater. Only 59 percent of schools with lower levels of standards coverage had pass rates of 75 percent or higher.

In interviews with teachers, the study found the exam to have other salutary effects. One teacher said "The exit exam has caused remarkable changes in the students' willingness to work." Another said the exam "gives meaning to graduation."

In San Francisco, some of the high schools rank at the very bottom of the state's Academic Performance Index. Many are chronic underperformers, where generations of students have been turned out on the streets, degrees in hand, but with little education.

This ritual deceit may make for happy graduation ceremonies, but it has consequences. According to scholars Stephan and Abigail Thernstrom, in today's America, people with similar skills and knowledge will have similar earnings. What separates the successful from the unsuccessful, then, is not a diploma gap, but a learning gap. This test won't make all graduates the same, but it will ensure a level of minimum competence that the system cannot.

San Francisco students could use all that the exit exam offers -- more coverage of the standards, greater incentive to work and the knowledge that their diploma signifies real achievement. The superintendent is nonplussed by one particular charter school's graduation results, but her failure to ask the same questions regarding the city's other high schools shows that she needs this test as much as anyone.

For the next two years, Ackerman must wonder about all the district's students, "how did they graduate?" With no meaningful, objective measure of what they learned, she will be at a loss. But when her sophomores walk across the stage in 2006, the first year that students will have to pass the exit exam to earn a diploma, the superintendent will have all the answers.

Matt Coxi is a public policy fellow in education studies at the San Francisco-based Pacific Research Institute. E-mail him at mcox@pacificresearch.org. .