WASHINGTON — Mary Beth Tinker looks like an ordinary, middle-aged woman. Nothing about her subdued clothing, hairstyle or mannered demeanor suggests she's an answer on law-school exams. Except for the black armband.

Then you hear her speak to students as she did Wednesday morning at Cardozo High School, and you understand she is the black armband, after all these years.

"Kids can shake things up! That's what we need today — to shake things up!" Tinker tells the 40 students, mostly African American or Latino, slouched at their desks, fanning themselves with notebooks, wondering what this woman's talking about.

Her classroom visit coincides with the celebration of Constitution Day. You know, our new national holiday? The holiday that Congress passed and President Bush signed into law last year? No?

Every Sept. 17, except this year when it was observed yesterday rather than today, all public and private schools and universities that get federal funds are required to teach the Constitution, one way or another.

Tinker talks the Constitution from the ground up. Maybe not exactly how the president and Congress envisioned, but these students start to get the message.

"What are some things that need changing?" Tinker's voice gets louder.

One student mumbles, "The war in Iraq."

Tinker shouts encouragement: "Yes, the war!"

"What else?" she asks.

Someone else yells, "Gas prices." A young man with rows of braids, wearing an orange polo shirt shouts, "Poverty!"

Bingo! "That's right!" says Tinker, pumped by the response. "Gas prices are going up and wages are going down. The rich are getting richer and the poor are getting poorer, have you noticed?"

"Uh-huh," comes a collective reply.

Tinker turns back the clock to another era troubled by social unrest and a war that grew bloodier by the day. 1964. Freedom Summer. Northern activists descend on the Deep South to register African-American voters.

"And then there was the war, the Vietnam War, just like now," Tinker says.

"That was the kind of situation we were facing," Tinker tells the now-attentive students. "This is a history lesson today. It's about the First Amendment. Revolution. Some things going on in the world today just ain't right. That's why I'm wearing a black armband today."

When she was an eighth-grader 40 years ago at Harding Junior High in Des Moines, Iowa, her school suspended her for speaking out.

In 1964, Tinker was 13, one of six siblings whose father, Leonard, was a Methodist preacher teaching Quaker peace activism. He and his wife, Lorena Jeanne, taught their children to turn ideals into action. "And that was when the Vietnam War was on TV and we were watching it every evening," she says.

Tinker, her brother John, then 15, and other students decided to wear black armbands to protest the war. The Des Moines School Board got wind of the upcoming protest and threatened to suspend students who wore them.

"I decided to wear the armband anyway," Tinker says. She and four other students were suspended until they agreed to return without armbands.

The American Civil Liberties Union helped file a complaint at U.S. District Court arguing the protest was free speech protected by the First Amendment. They lost there and at the appellate court.

But in February 1969, the Supreme Court upheld the students' rights to free speech. In Tinker vs. Des Moines School District, Justice Abe Fortas wrote the landmark opinion that neither students nor teachers "shed their constitutional rights at the schoolhouse gate."

"I didn't realize for many years the significance of the case," says Tinker, who in the years since continued campaigning for peace and equal rights while working as a nurse, now in Los Angeles.

She has been speaking to students about the First Amendment and the Constitution for 15 years. She carries a pocket-size Constitution with her, so she can hold it up when talking to classes: "I feel this is as important to their health as getting their vaccinations."