As the commissars of political correctness on the left and the fundamentalist sentries of morality on the right have clamped down on the education system, more and more subjects, words and ideas have become taboo. According to Diane Ravitch's fiercely argued new book, "The Language Police," the following are just some of the things students aren't supposed to find in their textbooks or tests:

¶Mickey Mouse and Stuart Little (because mice, along with rats, roaches, snakes and lice, are considered to be upsetting to children).

¶Stories or pictures showing a mother cooking dinner for her children, or a black family living in a city neighborhood (because such images are thought to purvey gender or racial stereotypes).

¶Dinosaurs (because they suggest the controversial subject of evolution).

¶Tales set in jungles, forests, mountains or by the sea (because such settings are believed to display "a regional bias").

¶Narratives involving angry, loud-mouthed characters, quarreling parents or disobedient children (because such emotions are not "uplifting").

Owls are out because some cultures associate them with death. Mentions of birthdays are to be avoided because some children do not have birthday parties. Images or descriptions of a mother showing shock or fear are to be replaced by depictions of both parents "expressing the same facial emotions."

Mentions of cakes, candy, doughnuts, french fries and coffee should be dropped in favor of references to more healthful foods like cooked beans, yogurt and enriched whole-grain breads. And of course words like brotherhood, fraternity, heroine, snowman, swarthy, crazy, senile and polo are banned because they could be upsetting to women, to certain ethnic groups, to people with mental disabilities, old people or, it would seem, to people who do not play polo.

In "The Language Police," Ms. Ravitch — a historian of education at New York University and the author of "Left Back," a 2000 book about failed school reform — provides an impassioned examination of how right-wing and left-wing pressure groups have succeeded in sanitizing textbooks and tests, how educational publishers have conspired in this censorship, and how this development over the last three decades is eviscerating the teaching of literature and history.

The "bias and sensitivity reviewers" employed by educational publishers, she argues, "work with assumptions that have the inevitable effect of stripping away everything that is potentially thought-provoking and colorful from the texts that children encounter," and as a result, school curriculums are being reduced to "bland pabulum."

Ms. Ravitch — who served as an assistant secretary in the federal Education Department under President George H. W. Bush, and who was nominated by President Bill Clinton to the National Assessment Governing Board, which supervises national testing — writes with enormous authority and common sense. She shows how priggish, censorious and downright absurd "the language police" can be, and she does so with furious logic.

Though many of the broader points she makes here have been touched on by other writers — most notably, Frances FitzGerald in "America Revised: History Schoolbooks in the 20th Century" (1979), Jonathan Rauch in "Kindly Inquisitors: The New Attacks on Free Thought" (1993) and Joyce Appleby, Lynn Hunt and Margaret Jacob in "Telling the Truth About History" (1994) — she uses her own knowledge of the education system and a careful reading of current educational material to show just how institutionalized censorship is becoming.

Why have textbook publishers capitulated to, even embraced, bias guidelines and language codes? Why have they caved in to pressure groups by bowdlerizing texts, whitewashing history and eviscerating prose?

"The short answer is that they want to sell textbooks," Ms. Ravitch writes, "and that they must respond to the demands of their marketplace. To succeed in this highly regulated and politicized environment, it is essential for education publishers not to become embroiled in controversy." Because textbooks are so expensive to develop and because their success depends on the decisions of education officials in a few large states (especially California and Texas), publishers are susceptible to the demands of a small number of highly vocal pressure groups.

What these groups on both the right and left have in common, Ms. Ravitch notes, is that they all "demand that publishers shield children from words and ideas that contain what they deem the `wrong' models for living." Both sides "believe that reality follows language usage," that if they "can stop people from ever seeing offensive words and ideas, they can prevent them from having the thought or committing the act that the words imply."

While censors on the right aim "to restore an idealized vision of the past, an Arcadia of happy family life" in which Father knows best, Mother takes care of the house and kids, and everyone goes to church on Sundays, censors on the left believe in "an idealized vision of the future, a utopia in which egalitarianism prevails in all social relations," a world in which "all nations and all cultures are of equal accomplishment and value."

In trying to promote such ideal worlds, censors on the right and left often end up demanding texts that are not realistic, as any child, exposed to television, pop music and the daily hubbub of real life can plainly see. When it comes to the teaching of literature, it can reduce the ambiguities and complexities of art into simplistic social and political messages; it can result in the rejection of classic texts and good writing in favor of boring works, calculated to offend and stimulate no one; and it can result in the selection of works deemed "relevant" to students, instead of works that might broaden their outlook and introduce them to new worlds.

As for the teaching of history, Ms. Ravitch argues, the sort of censorship being practiced today by textbook publishers can result in all manner of distortions and simplifications. For instance, to insist that depictions of women as nurses, elementary-school teachers, clerks, secretaries, tellers and librarians perpetuate demeaning stereotypes is to minimize "the barriers that women faced," and to pretend "that the gender equality of the late 20th and early 21st centuries was a customary condition in the past."

At the end of this book Ms. Ravitch makes three suggestions for stopping censorship within the educational system: namely, "disestablishing and deregulating the textbook adoption process" so that teachers rather than state officials decide what books will be chosen and the leverage of political pressure groups is diminished; creating mechanisms to expose to public view what publishers, the states and federal government are doing with educational material; and finding better-educated teachers "who are masters of what they teach."

A fourth suggestion might be added to that list: reading "The Language Police" as an introduction to the problem, a book that is every bit as alarming as it is illuminating.