Librarian Michelle Cowell was telling her eighth-grade students that anyone in the world could edit the free online encyclopedia Wikipedia when one boy started giggling.

"Ooh, I just changed it," he announced. Within five minutes, two more students had altered a Saddam Hussein article.

"The first thing they did was change it to say, 'He has bad breath,' 'He has stinky feet,' " said Cowell, of Waverly-Shell Rock Junior High in Waverly, Iowa. She didn't approve, but had to admit: "It is real easy. It kind of proved my point for them."

Search the Internet for any word and it's likely a Wikipedia link will pop up. It's the most popular Internet reference site, ahead of Yahoo, and the American Library Association ranked it among the best. Kids use it. Some teachers use it. Even congressional documents cited it recently as a reference on congressional apportionment. But its easy and frequent manipulation has school librarians across the country debating its utility for students.

Along with being edited by anyone, it can be edited at any time, which means the original source could change before a student's English essay lands on a teacher's desk. Professors write Wikipedia articles. Then again, so do high school students.

"It's a new technology that we're all looking at and trying to determine how it can best be used in an instructional setting," said Linda Williams, president of the American Association of School Librarians. "Some people think it can, some people think it can't."

Wikipedia founder Jimmy "Jimbo" Wales said the average quality of the articles is high, pointing to the science journal Nature's 2005 study showing science entries were almost as accurate as the Encyclopedia Britannica's. But vandalism is routine, forcing site volunteers to block hundreds of computer addresses each day, Wales said. "Because it is a work in progress," he said, "sources should be checked."

Stoking the librarian debate was the revelation in late January that congressional and Senate staffers removed negative references in articles about their bosses and apparently vandalized some senators' pages. (Sen. Tom Coburn, R-Okla., got tagged a female-hygiene device and the age of Sen. Robert Byrd, D-W.Va., was listed as 180.)

After a newspaper exposed that one congressman's biography was written by his staff in defiance of the site's neutrality rule, Wikipedia investigated and found more than 1,000 edits from congressional and Senate computer addresses.

With so many reliable Internet resources, librarian Cheryl Quinn from St. Viator High School in Arlington Heights, Ill., asked "Why bother with it?"

Quinn said she hopes to send students to Northwestern and Notre Dame universities, and "their professors are not going to be impressed with Wikipedia as a resource."

Even so, students are bothering with it. "Who doesn't look in Wikipedia?" is what librarian Tish Carpinelli heard while discussing the topic with Advanced Placement English students at Lower Cape May Regional High School in New Jersey.

At least one of her students, Michele Robinson, doesn't use it. She looked up an entry about Cape May a year ago and found a horrific story about the town's buildings being made from burned bodies — fiction she later learned was the work of one of the school's graduates. "I was just like, I'm not using this," she said.

But Diane R. Chen, a librarian at Hickman Elementary School in Nashville, Tenn., said she believes Wikipedia has its uses. It helped answer her kindergartners' questions about monarchies, something the school's curriculum didn't adequately cover.

On a school librarian e-mail group, she wrote that librarians risk being viewed as "dated and out of touch" by blocking or arguing against Wikipedia as a secondary resource. "Citizens have the desire to participate in the creation of knowledge. This is a worldwide trend. It is time for us to ramp up our work in teaching evaluation of material but not to prohibit access to Wikipedia," she wrote.

For information on any Web site, teachers should ask students about the author's credentials and whether they cross-referenced information with other sites to determine its accuracy, said Dennis Van Roekel, vice president of the National Education Association.

Peggy Sheehy, media specialist at Suffern Middle School in New York, said she does this, showing her students Web sites that portray the fictional "jackalope" animal as real and asking, "How do we validate this?"

But librarians said some teachers, not all, are among those who need to learn more about Wiki-pedia. Annapolis (Md.) Senior High School teacher Neill Russell agreed. He was saying Wikipedia was "one of the best sources out there" — until he learned it could be edited by anyone.

"I think teachers like myself, that are having kids do research, we're not aware of it," said the earth science and astrology teacher. "I'm going to take a look at it tonight. I didn't know they could do that."

Despite the debate, collaborative authoring sites known as Wikis may be finding their place in education. Matt Barton, a new assistant English professor at St. Cloud State University in Minnesota, gave students in his computers-and-English class a Wiki assignment during his first semester of teaching. They created a composition textbook on "Wikibooks," a sister project to Wikipedia, and got feedback from around the world. Now, a textbook that might cost $70 in print is online for free, he said.

Barton, himself, likes Wikipedia's format.

"There's no passwords, there's no top-down control," he said. "It's just people interested in knowledge."