by Alfie Kohn.

256 pages. DaCapo. $24.

 To paraphrase a comment about Thomas Babington Macaulay, the famously self-confident 19th-century British historian, I wish I were as sure about anything as Alfie Kohn is about everything.

Kohn, a Massachusetts-based education writer (and Brown University graduate), has written nearly a dozen books that stake out his militantly “progressive” position. In Kohn’s Manichean educational world, everything is either good or bad. Among the latter: “teacher-centered” instruction, memorization, standardized tests, and even desks in rows. Now he’s taking on homework. All homework. At any grade level. In any form. Like Groucho in Horsefeathers, whatever it is, he’s against it.

According to Kohn, it has never been demonstrated that homework improves student achievement or habits. He cites studies, particularly ones that focus on the elementary grades, that support his argument, or at least don’t contradict it, and he’s persuasive when arguing that elementary students are bearing a substantially heavier homework load than they did years ago.

So I am not entirely unsympathetic to Kohn’s argument that younger children, at least, are “missing out on their childhoods.” I’ll even try to overlook over-the-top rhetoric, such as saying that a policy of “high-stakes” exit exams “threatens to create nothing short of an educational ethnic cleansing in America.”

As a teacher, parent, and longtime reader of books like this, however, I can’t help but wish Kohn considered all the evidence about how much homework our students do. For instance, what about two large, recent surveys indicating that most high schoolers spend less than an hour a night on homework? Alexandra Robbins’ new book, The Overachievers, depicts high school students obsessed with getting into selective colleges as staggering (literally and figuratively) under their workloads. But the great majority of their peers take a lot more time for TV and video games than for schoolwork.

Finally, there’s the issue of homework versus “busywork.” Who among us — as student or parent — has not encountered the truly mindless homework assignment? I still recall a ninth-grade science class project that put us into teams of three; each student was to outline the lives of 32 famous scientists, then copy the outlines made by the other two, and hand in all 96. I can still feel the writer’s cramp.

Kohn seems to think it’s all like that. But there are far more useful, justifiable activities, and only in the book’s last two chapters does Kohn — very grudgingly — talk about some (temporary) accommodations he’s willing to make. Too little, too late.

These days, conversation about many public issues, including education, is dominated by noisy extremists who caricature the opposition, cherry-pick evidence, and force complicated realities into convenient ideological slots. Given his energy and resourcefulness, it’s unfortunate that Kohn is content to be the Michael Moore of K-12 education.