Caleb Stewart Rossiter, a college professor and policy analyst, decided to try teaching math in the D.C. schools. He was given a pre-calculus class with 38 seniors at H.D. Woodson High School. When he discovered that half of them could not handle even second-grade problems, he sought out the teachers who had awarded the passing grades of D in Algebra II, a course that they needed to take his high-level class.

There are many bewildering stories like this in Rossiter’s new book, “Ain’t Nobody Be Learnin’ Nothin’: The Fraud and the Fix for High-Poverty Schools,” the best account of public education in the nation’s capital I have ever read. It will take me three columns to do justice to his revelations about what is being done to the District’s most distracted and least productive students.

Teachers will tell you it is a no-no to ask other teachers why they committed grading malpractice. Rossiter didn’t care. Three of the five teachers he sought had left the high-turnover D.C. system, but the two he found were so candid I still can’t get their words out of my mind.

The first, an African immigrant who had taught special education, was stunned to see one student’s name on Rossiter’s list. “Huh!” Rossiter quoted the teacher as saying. “That boy can’t add two plus two and doesn’t care! What’s he doing in pre-calculus? Yes of course I passed him — that’s a gentleman’s D. Everybody knows that a D for a special education student means nothing but that he came in once in a while.”

The second teacher had transferred from a private school in a Southern city so his wife could get her dream job in the Washington area. He explained that he gave a D to one disruptive girl on Rossiter’s list because, Rossiter said, “he didn’t want to have her in class ever again.” Her not-quite-failing grade was enough to get the all-important check mark for one of the four years of math required for graduation.

Rossiter moved to Tech Prep, a D.C. charter school, where he says he discovered the same aversion to giving F’s. The school told him to raise to D’s the first-quarter failing grades he had given to 30 percent of his ninth-grade algebra students. He quit instead.

Tech Prep officials indicated the F’s would have violated special-education rules. A D.C. schools spokeswoman said that Rossiter is not a credible source and that D.C. academic progress is shown by rising standardized test scores.

I share Rossiter’s view that such rule-bending is common in many D.C. schools overloaded with struggling students. The trend has been aggravated by computerized credit-recovery courses that take a few weeks and allow students to escape high school lives they loathe. Former D.C. history teacher Erich Martel has done much research on this. I have pointed out that the educators enabling such grade inflation might have the students’ best interests at heart. The students won’t stay in school, so giving them a diploma, no matter how fraudulent, might provide them with a chance to get some kind of job and, eventually, as they mature, sort themselves out.

It is very hard to maintain that Pollyanna-ish take on grade inflation after reading Rossiter’s book. He wrongly overlooks or discounts evidence of improvements in teaching and learning in many schools here and elsewhere, but his main point is unassailable. Lying to so many students, their families and other teachers is wrong and yet is rarely discussed in professional circles.

High school graduation rates, as reported by school districts with no independent checks, have been climbing. Public school officials said the D.C. graduation rate increased five percentage points in the past four years. The U.S. rate rose from 74 percent in 2007 to 81 percent in 2012, according to the Education Week Research Center.

I know of no research on how much of that increase can be attributed to fantasyland report cards. Rossiter says the strongest blow against fraud would be to reverse the national trend toward insisting that every high school student get a college-preparatory education before graduation.

I thought that trend was good. Most of those courses also help in the workplace. But Rossiter’s book is forcing me to reconsider.