A year after more than two dozen Asian American students were attacked at a high school in South Philadelphia, the Justice Department has reached an agreement with school officials there, resolving a high-profile investigation into school bullying.

The Philadelphia incident, which involved a day-long assault on the students and sent 13 to the hospital, was one of several glaring cases of school harassment across the country last year. The attack made international news when it triggered an eight-day boycott by Asian American students, many of them recent immigrants, who said they would not return to school until they felt safe.

Justice Department officials signaled that the agreement with the School District of Philadelphia, which requires the district to hire a consultant focused on preventing harassment and discrimination, will serve as a nationwide standard for school systems trying to prevent bullying. Student-on-student harassment is an increasing problem and makes up a growing portion of the cases under investigation by Justice.

"We intend to use every tool in our law enforcement arsenal to stamp out harassment and bullying in the schools," said Thomas Perez, chief of Justice's civil rights division. "School districts are accountable for creating policies, practices and a climate of inclusion and . . . if a school district deliberately ignores instances of harassment" based on race or sexual orientation, he said, "they do so at their peril."

The Justice Department agreement, which is similar to one the school reached with the Pennsylvania Human Rights Commission, requires Philadelphia schools to develop a plan for preventing bullying; conduct training to increase multicultural awareness; and maintain records of harassment. The settlement agreement, which must be approved by a Philadelphia federal court, will remain in effect until June 2013.

Advocates of the students said the attack, which occurred Dec. 3, 2009, was part of a pattern of racial harassment and violence at South Philadelphia High School that goes back at least to 2007. Complaints were filed with school officials but were met with indifference and intentional disregard, according to students.

On the morning of Dec. 3, teachers and students witnessed groups of African American students searching classrooms for Asian American students, according to the complaint filed by attorneys for the students who were attacked. Throughout the day, students and teachers raised concerns about safety with school security and administrators but no moves were made to protect the students, the complaint said.

In the complaint, the attorneys described a scene in which "a group of Chinese students was escorted to the cafeteria by a school security guard. After entering the cafeteria, this same group of Chinese students saw that the cafeteria was chaotic and turned around to leave the room. However, as they were leaving, a group of students attacked them from behind and began punching and kicking the Chinese students. At least one student suffered a black eye, trauma to his head, and serious bruises on his hip, arms and hand."

Similar incidents continued throughout the day. Even before the melee, Asian American students said they were teased because of their accents, the way they dressed and their friends.

The Asian Student Association of Philadelphia, which led the student boycott, said in a statement that "many people tried to tell us that it was not racial what was happening to us. But what people have to understand is that Asian youth do suffer from racial bias, from people calling them names and adults not doing anything."

Duong Ly, a Vietnamese immigrant and senior at the school, said his brother was pushed against a locker twice and hit from behind on the head by a student he could not identify.

"I went to school every day being scared, wondering when would be the next time I'd be attacked because I knew that a lot of my friends had been attacked," Ly said. "I was often laughed at because of who I was."

Changes have been made at the school, which has a new principal, and Ly said he is more comfortable there.

"Today we witness our own victory," he said.

Members of the Asian student group praised the agreement and said they hoped it would bring attention to gay and lesbian students who have been harassed arcross the country. "Many . . . have committed suicide because nobody spoke up against bullying. We hope that we can share this victory with all those students who have been victims of bias," the students said.

Cecilia Chen, staff attorney at the Asian American Legal Defense and Education Fund, which pushed for the investigation, said Asian American students have been dealing quietly with harassment for years. "It is an issue that is pervasive and often overlooked by school," she said. "This really sets a strong precedent for how schools have to respond to harassment when it occurs. They cannot turn a blind eye."

Perez said the civil rights division has several pending bullying investigations and plans to continue pursuing the issue.

"If we don't address this in the middle school and high school, then we will build and foster a culture of intolerant adults," he said.