A popular professor at the University of Massachusetts at Lowell was hospitalized and one of her students is in jail after an incident Thursday in which police say the student knifed his professor in a dispute over a failing grade. The attack has raised anew the difficult question of how colleges can protect their professors from potentially lethal altercations with students.

Mary Elizabeth Hooker, an associate professor of clinical laboratory and nutritional sciences, has taught at Lowell for 12 years. William T. Hogan, chancellor at Lowell, issued a statement noting "her dedication and devotion to her job, her peers and her students." In a gesture that Lowell colleagues said was typical, she apparently brought snacks and coffee to class Thursday to mark the end of the semester.

According to police reports, later that day she was followed to her Cambridge home by Nikhil Dhar, an undergraduate at Lowell who was apparently angry about failing a course Hooker taught. Police reports say that Dhar stabbed Hooker, slashed her neck, ripped off her shirt and beat her. Neighbors stopped Dhar as he was fleeing, police said, finding Dhar covered in blood and Hooker bleeding from multiple wounds. (She is now out of the hospital and told a campus spokeswoman that she was looking forward to returning to campus.)

The Boston Globe reported that Dhar pleaded not guilty on Friday to charges of assault with intent to murder and assault and battery with a deadly weapon. A judge ordered Dhar jailed without bail pending a hearing today.The Globe quoted Dhar's lawyer, Stephen Hrones, as saying that his client went to Hooker's home to discuss his grade and that the situation was "more complicated" than police reports have indicated. Hrones told the newspaper that Dhar does not have a police record, is from Calcutta, and is in the United States on a student visa.

While physical attacks on professors by disgruntled students are not common, they do happen. In the last 10 years, professors have been killed by students or former students at the Appalachian School of Law, California State University at Los Angeles, San Diego State University and the Universities of Arizona and Arkansas at Fayetteville.

Ann Franke, president of Wise Results, a consulting firm that advises colleges on legal issues and risk management, has studied the issue of students who kill professors. She said that the norm in such cases is for the attacker to be male, for the attacks to happen on campus, and for the source of the students' anger to go well beyond a grade (although that may be a spark). "These are people who perceive themselves to have serious problems in multiple sectors of their lives," Franke said.

The difficult thing for colleges and professors, she said, is figuring out which students who are devastated by a grade or some academic setback present a true threat. Franke said one of the best resources to help colleges is a report produced in 2002 by the U.S. Education Department and the Secret Service, prompted by the 1999 killings at Columbine High School. The report, "Threat Assessment in Schools: A Guide to Managing Threatening Situations and to Creating Safe School Climates," focuses on high schools, but Franke said that many of the recommendations apply to colleges.

Franke recommended that colleges have special panels -- involving campus safety officers, counseling center officials, student affairs officers and others -- to evaluate situations involving students who may pose a threat. She said that many campuses do not create such panels until a tragedy takes places, leaving professors unsure about whom to contact if they are worried about a student or former student.

There are a range of steps such a panel might take or recommend, including seeking court orders to bar a student from campus or from a professor's office or home, requiring students to meet with a dean or counselor to talk about incidents that have taken place, or ensuring that a professor receives security protection. Even with experts, Franke said, "this is not an area where you can have 100 percent certainty."

Students who try to attack professors generally do provide "warning signs" but they aren't always identified until after an assault, said Greg Boles, global director of the threat management practice of Kroll Inc., which advises colleges, companies, and other organizations about threats.

Boles said that in many cases, it becomes clear after the fact that a student said something to a friend or another professor and the comment wasn't taken as seriously as it should have been. He said that a major warning signal is not necessarily anger, but a state of hopelessness. Professors or friends may think that by telling such a person "it's not the end of the world" that they are helping, but the problem may be the person's perception that a failing grade is in fact the end of their world.

Colleges may have a tougher time than businesses in dealing with these issues because of academe's "open culture," Boles said. But through the use of threat assessment teams, he said that colleges can improve their safety. He said that it was important not only to have the teams, but to be sure that there is a phone number that can be called 24 hours a day, and that calls can be placed anonymously, since some people are embarrassed to report their fears.

Franke's top recommendation for professors is that they trust their own instincts. "I would say that any faculty member who feels in his or her gut that a student's disgruntlement is out of the ordinary should report. People do have a gut sense and they should trust it."