Kimiya Haghighi, 17, had a prose problem. As much as her teachers preached concise writing, her sentences remained long and overwrought — the words poured out, unpunctuated, one after another.

Then Aubrey Ludwig, her 11th-grade English teacher at Langley High School, introduced her class to Twitter, requiring that students tweet their responses to a Hemingway assignment in 140 characters or less. Suddenly, Haghighi’s writing was efficient, declarative, even staccato. “It was a total breakthrough,” she said.

Such assignments are coming under new scrutiny as Virginia and other states consider restricting how teachers and students interact on social-networking platforms such as Facebook, MySpace and Twitter. Officials want to preserve the educational opportunity offered by Ludwig and other teachers but also want to prevent sexual predators from exploiting the casual tone of such sites to build rapport with potential victims.

The Virginia Board of Education voted Thursday to encourage school districts statewide to adopt policies regulating social-media use by teachers. The move was not as bold as an earlier proposal but still ranks the state as among the first to address such issues.

The push for new restrictions grew, in part, from the case of Kevin Ricks, a former Manassas High School teacher convicted last year of molesting a former student. Ricks exchanged personal messages with several students on Facebook, including the eventual victim.

Now, the debate over how to manage teacher-student contact on social-networking sites is expected to come before local school boards. “Any prudent board would look at crafting a policy on this,” said Sanford S. Williams, a Manassas school board member.

But advocates for stricter rules will face teachers who want to continue using social networking to help educate students.

“Part of my job is to get the students engaged,” said Ludwig. “It’s easier to do that if I can link the homework to Twitter and Facebook. The hope is that when it’s time for the AP exam, what started as a novelty will translate into a real skill.”

Some of Ludwig’s colleagues at Langley have taken a similar approach. English teachers Sandra Hamilton and Sara Vincent asked their students to create Facebook profiles for characters from “The Canterbury Tales,” Geoffrey Chaucer’s 14th-century collection of stories.

“I had to write interests and status updates for the friar in the story — he was like a total frat guy,” said Cyrus Kingdom, a senior. “It’s the kind of assignment I found interesting because I could relate to it.”

The assignment might be innovative but it’s not unique. Facebook is populated by dozens of Chaucer characters: the products of high school English assignments across the country.

Other teachers have formed Facebook groups for their classes, using them to post homework assignments, links to relevant articles and reminders about upcoming tests and due dates. Students are able to keep up with such postings without becoming Facebook friends with their teachers.

Virginia education officials, however, worry that such technologies open the door to potential offenders. The state recorded more than 120 cases of sexual misconduct between teachers and students over the past 10 years, the “vast majority” of which included texting and other forms of digital communication, according to Virginia Department of Education spokesman Charles Pyle.

Experts say that such contact makes it easier for predators to engage in what experts call “sexual grooming,” the first stages of an inappropriate teacher-student relationship.

The original version of the rules proposed by the state board would have made Virginia one of a handful of states to adopt firm restrictions on the use of social networking, but the opposition from teachers and local school officials forced a reconsideration.

“The board revised the policy, recognizing that it’s not practical to be too prescriptive in suggesting a model policy,” said Pyle.

Some experts on education and sexual misconduct saw great promise in the state’s initial guidelines and were disappointed by the weaker version adopted Thursday.

“The first guidelines looked out for children. The most recent guidelines look out for adults,” said Charol Shakeshaft, author of the U.S. Department of Education’s 2004 report on sexual misconduct and a professor at Virginia Commonwealth University. “Virginia would have been a leader. Not anymore.”

Some social-networking giants, meanwhile, have established education arms, explaining how their Web sites and mobile technologies might be useful teaching tools. But a cadre of other Web start-ups, hoping that Facebook, MySpace and Twitter won’t succeed in public schools, have begun marketing products tailored specifically to classrooms.

Schoology, Moodle and online education titan Blackboard now offer social-networking services made exclusively for educators and students. It’s a market that could expand significantly, depending on the policies that state and local governments pass in coming years.

In Louisiana, for example, instructors may only use electronic or digital tools “provided by or otherwise made available by the school system.” Other school districts ban Facebook, which they say raises concerns about security — not to mention productivity — but allow access to Schoology and Blackboard, where interactions between students and teachers are easier to regulate.

“It’s not about the technology, it’s about how it’s used, about acceptable behaviors,” said Kathy L. Smith, chairwoman of the Fairfax County School Board. “Somebody who wants to relate in that way is going to find a way to do it.”