The Declaration of Independence is a poor excuse for an obscure historical document. It's not the Magna Carta or the Peace of Augsburg. Its name is so straightforwardly functional, it almost makes you wonder why the Founders weren't more imaginative.

Yet only 35 percent of American fourth-graders know the purpose of the Declaration of Independence, according to the 2010 results of the National Assessment of Educational Progress. The findings of the test - administered to representative samples of fourth-, eighth- and 12th-graders - are another dreary recitation of the historical ignorance of America's students.

Only 20 percent of fourth-graders, 17 percent of eighth-graders and 12 percent of 12th-graders were proficient in history. More than half of 12th-graders were categorized as "below basic." Only 22 percent of 12th-graders knew that North Korea was allied with China during the Korean War. Education expert Diane Ravitch notes with dismay that 40 percent of these students were already eligible to vote when they took the test, and all will be eligible within a year.

They are the symptoms of a country engaged in a long process of erasing its memory. For decades, we have been congratulating ourselves for a broad-mindedness that is really a self-destructive national amnesia.

It's no accident that the teaching of American history became ascendant during the surge of national self-confidence in the wake of the Civil War. The late sociologist Samuel Huntington reported in his book Who Are We? that just six states required the teaching of history before the Civil War. By the turn of the century, 23 did.

Back then, we infused the endeavor with an unabashed love for America. Historian Merle Curti writes that the schools "emphasized the importance of presenting vividly and attractively to children the glorious deeds of American heroes, the sacrifices and bravery of our soldiers and sailors in wartime, the personalities of the presidents, who might properly be regarded as symbols of the nation in the manner in which royal personages of Europe were regarded."

A study of 400 textbooks published between 1915 and 1930 found almost all of them were robustly nationalistic, or as one scholar commented: "The American is taught to respect and to venerate his forebears and the institutions which they designed and developed."

How appropriate. How passé. Today, we're lucky if students can pick their forebears out of a lineup.

The content of education began to change in the middle of the 20th century and eventually tipped into embarrassment and self-abasement. Huntington cites a study of 22 grade-school readers published in the 1970s and 1980s. Out of 670 stories and articles in the books, only five were patriotic. All of the stories dated from before 1780. Four of them focused on a girl. Three of them involved the same girl, Sybil Ludington, the female Paul Revere.

As this transpired down below in the elementary schools, the professional historians worked to kill American history from above. They suffocated it first in data-driven "social history" and then in multiculturalism, until it seemed fit only for obsessives about race or gender.

This pincer movement has degraded our collective store of self-knowledge. Ravitch points out that students score better on math, reading, science, civics, writing and geography than on history. It is practically going the way of home ec.

The neglect of history leaves on the cutting-room floor all the entertaining, instructive and inspiring material involved in the world's most daring and (ultimately) successful experiment in self-government. Worse, it robs us of one of the most important constituent parts of our national identity.

Historian David Lowenthal says of heritage: "By means of it we tell ourselves who we are, where we came from, and to what we belong." Increasingly, we don't know and don't want to know. "Never forget" is an appropriate admonition for victims of atrocities. "Never remember" is a strange and ominous admonition for a nation somebody or other once called "the last best hope of Earth."

Rich Lowry is editor of National Review.