LOS ANGELES — Gizelle Studevent was a 13-year-old eighth-grader at prestigious La Jolla Country Day School in suburban San Diego when the harassment began. She returned from a basketball tournament to find an unsigned note in her suitcase: Addressed to "Senorita," it mocked the girl's skills on the court and suggested she go home to Mexico.

Over more than two years, an anonymous band of bullies tormented Gizelle. Their acts grew increasingly cruel — on the Internet, in notes and around school. Finally, she transferred.

"I would go home and cry every day," said Gizelle, now a junior at private Bishops School. "It was horrible. The scary thing for me was, what was next? What was going to happen?"

The 17-year-old is among a growing number of students who are reporting that they are victims of bullying, according to educators and experts. And bullying — once largely restricted to stolen lunch money or hallway shoving that was taken somewhat lightly — has grown increasingly serious, officials, parents and students say.

Today, parents are filing lawsuits against students and schools for failing to protect their children, administrators are taking stronger disciplinary action against perpetrators and a virtual industry of anti-bullying programs has sprung up.

In 2005, 28 percent of students age 12 to 18 reported being bullied in the previous six months — double the figure from four years earlier, according to the U.S. Department of Justice. The true figure is almost certainly higher; experts believe underreporting is rampant.

The consequences can be devastating and even deadly, as in the slaying of 15-year-old Lawrence King at a middle school in Oxnard, Calif. The teenager was shot in the head Feb. 12 in a classroom after being harassed by some classmates when he disclosed that he was gay.

State Sen. Sheila Kuehl, D-Calif., who pushed through legislation that added new protections against discrimination on the basis of sexual orientation and gender, said educators must act immediately to stop the first aggressive acts. Allowing this behavior to go unchallenged creates an environment in which it is seen as acceptable, allowing it to escalate, she said.

"They need to remove people that are doing this and deal with them and not turn a blind eye," Kuehl said. "These are not just youthful high jinks; these are dangerous situations."

Administrators and teachers were once reluctant to get involved, but that attitude has changed, most urgently after two bullied Columbine High School students massacred 12 classmates and a teacher before killing themselves in 1999.

Bullying is "a life-changing event," said Bakersfield attorney Ralph Wegis, who often represents students in cases against school districts.

He recently filed a lawsuit against the Kern High School District and several students on behalf of a teenager who he said was terrorized on a trip to a debate team competition. Staying in a hotel with Stockdale High School teammates, the then-14-year-old was allegedly bound with duct tape and plastic food wrap from his ankles to his shoulders. His mouth was taped shut, and his teammates took pictures and urinated on his clothing, Wegis said. The lawsuit is in the discovery phase; the district and its attorney declined to comment.

Experts insist more can be done. Because administrators face many obstacles in punishing students during off-campus activities, school violence expert Derek Randel suggests that schools require students who participate in extracurricular activities to sign pledges that specifically ban online bullying.

Anonymous ways for students to report harassment, including phone hot lines, might allow students to alert adults, without fear of retribution, when they or their friends are being bullied, he said.

Increased supervision in cafeterias, locker rooms and hallways is also key, Wegis said.

That's where Gizelle and her family say educators failed them. Despite pleas from her parents for an investigation, no student was ever punished.