A school system's graduation rate may be the ultimate measure of how it's fulfilling its promise to the community to turn out young adults ready for productive lives.

It's also a major measure of the federal No Child Left Behind Act, which requires every school system to have a 100 percent graduation rate by 2014.

But in Virginia, the rate is a faulty calculation based on an unaudited honor system of reporting that gets interpreted differently from one school division to the next and leaves untold numbers of students uncounted.

The Virginia Department of Education has lacked the ability to track individual students through public schools, so many who move from one district to another, or to private schools or out of state, are potentially unaccounted for and could even be listed as dropouts.

It's a problem the state is fixing, and 2008 will be the first year Virginia can provide an accurate graduation rate based on the tracking of individual students, said state Department of Education spokesman Charles Pyle.

Roanoke school officials make no denials that they have plenty of work to do on their graduation rate, but they say the flawed method of accounting makes comparisons to other divisions unfair and are an unreliable measure of the city's performance.

The issue is muddied further by the semantics of who is a graduate.

For its own purposes, Virginia counts eight different kinds of completion documents for high school students: standard and advanced diplomas, special diplomas and modified standard diplomas for students with disabilities, General Education Development test certificates, program certificates and others.

Completion documents such as special diplomas and GEDs are "bona fide options for some students," said Vella Wright, the Roanoke school system's head of accreditation, accountability and assessment. A standard diploma simply is not an appropriate expectation for some students, she said.

The public still thinks of graduates as students with standard or advanced diplomas, school board Chairwoman Kathy Stockburger said. "That's no longer an accurate perception of completion."

Yet that is exactly the definition of graduation that No Child Left Behind demands.

In Virginia, the NCLB rate is calculated as a fraction. The top number in the fraction, or numerator, is the total of standard and advanced diplomas.

The bottom number in the fraction, or denominator, is the total of standard and advanced diplomas, special diplomas, modified standard diplomas, GEDs, and all other forms of completion recognized in Virginia. Add to that number the dropouts from that year's graduating group of students as tabulated over each of the previous four years.

The rate is the percentage derived by dividing the top number by the bottom number.

In Roanoke last year, that number was 58 percent. For Patrick Henry High School it was 63 percent, and for William Fleming High it was 58 percent.

According to Wright, if you put all forms of completion recognized in Virginia into the top part of the fraction, you get a completion rate for Roanoke last year of 77 percent.

Yet all these calculations continue to be flawed because students who move, and even those who fall behind their classmates and graduate late, are unaccounted for, Wright said.

Stockburger argues that outside measures such as No Child Left Behind punish systems like Roanoke's that seek to get each student to an appropriate finish to his or her public school career, even if it's short of a traditional diploma.

The system is in effect punished for awarding special diplomas or routing potential dropouts toward GEDs, said Ed Holstrom, the city's director of professional development and school improvement, a former state Department of Education official. "We're risking failure."