A Fairfax County mother has been telling me about her bewilderment at her bright but school-hating daughter’s passing English even though her second-quarter and third-quarter grades were F’s and she skipped the final exam.

Having encountered earlier report card mysteries, the parent e-mailed all of her daughter’s teachers June 10, asking that she be given the marks she deserved. That didn’t happen, but at least the English teacher on July 9 sent her an honest explanation of why the frequently absent student got an A for the fourth quarter and scraped by with a final course grade of D.

The teacher confessed that the student did not earn that fourth quarter A but participated in several class discussions and demonstrated that she understood the bulk of the material throughout the year. Her problems, the teacher concluded, were lack of effort and attendance, not comprehension.

It was breathtaking to the Fairfax parent, as it would be to other mothers and fathers, to learn that the teacher could have justified a final grade of F but didn’t think there would be an academic benefit to failing the student. The daughter knew the material better than most of the students, said the teacher, who let her pass despite her misbehavior.

Astonishingly, the English teacher had a policy that the final exam score, no matter what it was, counted only if it maintained or raised the student’s overall grade. So blowing off the exam had no consequences.

I complained recently about D.C. schools’ giving D’s for no work to get as many uncooperative students as possible graduated so the schools wouldn’t have to deal with them anymore. I should have noted this also is a problem in some of our most affluent and well-regarded suburban schools, as the Fairfax parent’s experience makes clear.

Fairfax County schools spokesman John Torre said in that system “final grades may be based on trends in and mastery of learning rather than based solely on numerical averaging of quarterly grades for the year. A teacher may decide to limit the impact of a final exam grade if they feel it does not represent a student’s mastery of the content. Limiting the impact of a final exam grade does not mean the final exam score only counts if it maintains or raises a student’s overall grade. That’s not the district’s policy.”

The Fairfax student was delighted with the results, telling her parents she might hold the world record for getting passing grades despite doing nothing. Her parents want her to grow up. They wonder why the school system won’t help.

“If she still hasn’t mastered the skills or tackled the assumed requirements for a high school diploma — such as writing a paper, exploring historical periods, reading the classics and presenting a project — she will never succeed in college,” the mother said.

The student didn’t really pass geometry this year, either, even though she got a passing grade, but her parents decided not to press that issue because another of their children would be in geometry next year and they thought that would demoralize her. She passed another English course despite having F’s for the second, third and fourth quarters, which the parents also did not like. Despite their efforts to get the school to take her class-cutting seriously, it took at least 23 unexcused absences before a truancy officer was alerted.

Torre said the school system is examining its policies “in an effort to establish more consistent and equitable grading practices throughout middle and high schools.”

It is difficult to know what schools do nationally because there is little research on grading, but my impression is that policies are wildly inconsistent and that individual teachers often can do whatever they want.

I have long been sympathetic with high schools that think it is better to give diplomas to students who resist school rather than forcing them to sit in class, resentful, and then drop out with even less of a chance of getting a job. But couldn’t they help parents trying to motivate difficult teenagers by giving their grading standards a little backbone, just to see whether some students might find a spark of motivation to come to class and take the final exam?