Dan Janke knew something was wrong when he walked into the principal’s office and found the superintendent waiting for him.

When Janke sat down, the school administrators delivered a shocking message: Janke, an art teacher in the New Ulm, Minn., public schools, was suspected of sending sexually explicit e-mails to sixth-grade girls.

Janke was sent home that afternoon, suspended while police investigated.

Within days, the truth came out. Two seventh-grade boys had posed as their teacher in an online chat with the girls.

Every teacher can recall times when a student has tried to get even. But the revenge assumes a new dimension online, where children raised in front of the computer often hold the upper hand.

From New York to California, students are facing suspension, expulsion and even criminal charges for online spoofs targeted at teachers and school officials.

In Florida, a high school English teacher sued a student who she said posted her picture online, along with sexually explicit comments.

This month, some Coon Rapids middle-schoolers got a bogus e-mail purportedly from one of their teachers, inviting them to visit him on MySpace.

When they clicked on the link to the popular networking site, they were taken to a Web page filled with pornography and hate speech.

Other assaults come on Web sites such as Ratemyteacher.com, where students can grade their teachers on a scale of 1 to 5, complete with nasty comments and frowning cartoon faces.

For educators, Internet harassment is “one more stressor to add to a very stressful job,” said Sandy Skaar, president of Anoka-Hennepin Education Minnesota, the teachers’ union in the state’s largest district.

A student with a grudge – or playing a misguided joke – can put out a damaging message to thousands of people. With the Internet, adolescents have a powerful megaphone.

Do they have the maturity to use it responsibly? Janke doesn’t think so.

“We don’t let people drive until they’re 16,” he said. “They can’t vote until they’re 18, and they can’t drink until they’re 21. Yet kids in the third grade are on the Internet.

“We have given them this big responsibility, when they’re not ready for it without proper supervision and training,” Janke said. “It’s a dangerous thing.”

Teenagers operate in a different world from adults, said Ascan Felix Koerner, a University of Minnesota professor who studies adolescent communication.

“The moral compass fails them sometimes, and they’re not fully appreciative of the consequences,” he said. “They might create a website, and their peers would take it as a joke, and they perceive that adults would take it that way, too.”

Kirk Bauermeister didn’t know he was on MySpace until his teenage daughter told him. Students at the middle school in Costa Mesa, Calif., had created a fake MySpace site for Bauermeister, the school principal.

“The anonymity of it makes it real scary,” Bauermeister said. “It gives people the ability to do and say things they’d never do in real life.”

Many schools have blocked access to MySpace on school computers, but Bauermeister said it’s often futile: “As soon as we block it, they find a way around it.”