District teacher Erich Martel became suspicious during last year's Wilson Senior High School graduation when a student he had just flunked walked across the stage in cap and gown.

Martel went back and checked the student's records. He discovered that the F he had given her in Advanced Placement U.S. history had been erased. A different grade and course were listed: a D in U.S. history, just enough to allow her to graduate.

An assistant principal later acknowledged making the change and was disciplined for violating school policy.

But a broader mystery remains. The incident Martel uncovered is one of at least 11 cases in which Wilson students' grades were raised without their teachers' knowledge, according to school records and interviews with teachers. The cases occurred over the past three years and involved nine students, all of whom were Wilson seniors this year or last year.

School Superintendent Paul L. Vance is investigating those and other alleged irregularities involving student transcripts at Wilson, generally regarded as one of the city's top public high schools. "I consider the allegations very serious," said Steven G. Seleznow, the school system's chief of staff, who is overseeing the investigation.

Altering a grade without a teacher's involvement violates the D.C. teachers' union contract with the school system.

Martel, who brought the incidents to school officials' attention, said he is mystified and furious that an unseen hand eroded the standards he and other teachers seek to uphold.

"It was a feeling of being sabotaged, a feeling of being undermined, that for reasons that have nothing to do with the student's performance, there are shortcuts around a teacher's legitimate grade," Martel said.

Martel began reviewing the records of Wilson students on his own after the episode at last year's graduation, using a school computer system to spot instances where grades were changed and also looking at paper records. He provided copies of transcripts and computer printouts to The Washington Post after removing the students' names.

Of the 250 to 300 cases that he reviewed, Martel said, he found 29 Wilson grades that appeared to have been improperly inflated. In 11 of those cases, teachers confirmed to a reporter that the grades they awarded were later boosted without their knowledge. In the other 18 cases, the teachers involved either did not return phone calls or could not be located.

Four of the students whose grades were raised without their teachers' knowledge would not have been able to graduate last year without the change, according to the records Martel provided.

Teachers across the country have complained that they often face intense pressure from parents and students to change a grade. But when grades are changed, the principal usually makes the decision, according to national union officials. District teachers said many of the changes that Martel discovered would not typically have come to anyone's attention because teachers usually do not look at student records to verify that the grades are accurate.

Stephen Tarason, principal of the 1,650-student school, said he did not authorize any of the alleged grade changes and does not know what happened. "My concern is, are these being done purposefully?" Tarason said. "If they are, I will take action."

Tarason said that only a small group of administrators had access to the computer system to change grades. To prevent additional problems, he has further limited access and changed the passwords needed to enter the school's grades database. The computer system does not record the identity of the person who makes alterations to the database, and Tarason said it is possible that some of the changes were caused by a computer glitch rather than by an individual. He also suggested that in some cases the teachers involved may have forgotten that they approved the grade changes.

The 11 unauthorized changes that were confirmed through records and teacher interviews involved nine instructors. Most of them said they learned that their original grade had been raised only after Martel brought it to their attention.

One of the teachers, Anexora Skvirsky, said she gave a student a D in Spanish and the student's father later protested, pleading that his daughter was going to college and needed a high grade-point average. Skvirsky said she agreed to give the student a new final exam. But the student received an even lower score, so Skvirsky said she decided to leave the D alone.

Then she learned from Martel's research that someone had changed the D to a P for "Pass" -- even though P is a grade that school system's chief academic officer says is not allowed.

"I could not believe it," Skvirsky said. "I am absolutely alarmed. It is uncalled for. It is intolerable. It's like cheating. It's like lying. It's like fraud. And I am really absolutely angry to be associated with an institution that does things like this."

Wilson teacher Damian Kreske said two of his students' grades were changed in a zoology class. He said the first student came to class for only three weeks of the semester and the second student "disappeared from class the second half of the semester and never returned."

He said he gave the first student an F, which was later changed to a D, allowing the student to graduate last year. He gave the second student an I for "Incomplete," which is supposed to become an F if the student fails to finish the work. But the grade was changed to a C. That student is to graduate this year.

"I was upset when I found out my grades were changed," Kreske said. "It certainly made me question the importance of what I was doing in the classroom."

In the case involving Martel's student, the grade was altered by a Wilson assistant principal, Erasmo Garza, who has since been appointed principal at the District's H.D. Cooke Elementary.

Before attending Wilson, the student had taken a half-credit of U.S. history at a school overseas and received a C+. So Garza averaged the C+ with the F from Martel's class and created a new course listing on the report card with a passing grade of D.

"We're talking about the day before graduation," Garza said. "That's the only thing the child needed to graduate. I thought I was doing the right thing."

School officials said Garza was disciplined in the incident, declining to specify what penalty he received. Garza acknowledged that he failed to follow proper procedures in that case. But he said he was not involved in any of the other cases that Martel has brought to the school system's attention.

One student's grade was changed twice. The student received an F in an AP U.S. history class last school year. In September, the teacher discovered in school records that the grade had been bumped to a D+ and wrote a memo to an assistant principal, Helane Miller, requesting that the grade be changed back to F.

That change was made, school records show. But in January, the teacher discovered that the grade again had been turned into a D+, prompting him to write another memo to Miller. Once again, the grade was changed back to an F.

"This is a terrible corruption of the system and the academic process," said the second memo from the teacher, who agreed to be interviewed about the case on the condition that he not be named. "It must be corrected and this practice of unauthorized grade changes must be stopped."

Barbara Bullock, head of the Washington Teachers' Union, said she hears occasional complaints about grades being changed improperly. She said the school system needs to hold accountable those who violate the teachers' contract by making such changes.

"It doesn't help the child," Bullock said. "They're going around in life saying, 'I can get something for nothing.' . . . It tells the teacher that you do not value them as a professional."

Bullock said there were several earlier complaints of grade changes at Wilson that involved the school's former principal, Wilma Bonner, who now serves as an assistant superintendent overseeing the city's high schools. In two cases where grievances were filed, an arbitrator sided with the union and against Bonner.

Bonner said she changed grades in those cases after determining that the original grades were unfair. But she said she thought that she was following school system procedures and that the teachers were aware of the changes.

Martel also has raised questions about several dozen other students who graduated from Wilson last year or are set to graduate this year, citing records that suggest they were improperly given credit for meeting graduation requirements. Those cases, too, are part of an investigation that is focusing first on the records of this year's prospective graduates and will then expand to last year's graduates.

For example, Martel uncovered records suggesting that courses were put on students' transcripts even though they never took the classes, and that students who took the same course several times were awarded multiple credits.

But Tarason and other school administrators said they have determined that in many of those cases, Martel did not look at additional documents that show the students were properly credited.

Martel said he also found cases in which Wilson inflated the grades that students received at a school they previously attended. The records from the previous school showed one grade, while the Wilson transcript -- the document provided to colleges and used to calculate grade-point averages -- listed a higher grade for the same course. Wilson administrators could not explain those discrepancies last week.

Another complaint from Martel involves a world geography class taught at Wilson this semester. Records showed that 61 students were enrolled in the class, but the classroom that was listed could have accommodated only a fraction of that number, he said.

Tarason said the class was an independent study program in which students were given work to complete on their own time. Wilson's regulations disallow independent studies, however.

The principal said that after Martel's complaint, he canceled the course for freshmen through juniors but allowed seniors to remain if they needed the credit to graduate. He said he was convinced that those students were completing course work. The teacher who created the class, Clifford Dahlgren, did not return phone calls.

History teacher Erich Martel found that 29 student grades had been changed improperly at Wilson Senior High School.Erich Martel said the discovery that a grade had been changed gave him "a feeling of being sabotaged, a feeling of being undermined."