Around 11 a.m., a trash fire was set in an unoccupied classroom, one in a series of small blazes set by students in protest of the removal of the principal this week. Students were evacuated onto 48th Street, and when one teacher tried to tell students to get off a car, a ninth-grade girl punched him in the jaw, police said.

Another girl and a boy also tried to hit the teacher, Hubert Morton, 53, a long-term substitute.

Morton was taken to the Hospital of the University of Pennsylvania, where tests were being performed last night.

Police arrested one girl and as of last night were waiting for warrants to arrest two other students, all of whom are freshmen. Two juveniles, students at a nearby disciplinary school, were arrested and charged with trespassing for entering the 1,500-pupil school after it had been evacuated.

Outside the school, school district and Philadelphia police stood sentry. During the evacuation, they blocked off 48th between Walnut and Locust Streets and tried to keep order among the teeming, screaming students.

"We've been here quite a lot in the past couple months," Police Capt. Michael Sinclair said. "There's zero tolerance. We will make arrests."

Sinclair said police had made 30 arrests at the school since January.

The assault came three days after the school district spelled out tougher penalties for students districtwide who attack teachers - automatic 10-day suspensions pending expulsion to a disciplinary school, plus automatic felony charges of aggravated assault. The district also launched a teacher-safety hotline.

Responding to the turmoil at West Philadelphia, school chief executive Paul Vallas said he was taking steps to make the school smaller and safer. Vallas said he was breaking the school's acclaimed Academy for Automotive and Mechanical Engineering off as a separate school and, in September, would convert two area middle schools into small high schools to keep the population low at West.

Vallas said he had planned to make Shaw and Sulzberger Middle Schools into high schools and would accelerate those plans. The two schools will begin admitting ninth-grade students in September.

Beginning Monday, 12 members of the West Philadelphia Coalition, a community organization, will monitor the hallways at West Philadelphia High. They will join 13 school police and community members already at the school.

"They'll have considerably more resources to address the student climate issue," Vallas said.

Vallas said he believed that Ozzie Wright, one of two principals brought in to replace the ousted Clifton James, would ultimately calm things down. Wright, an former Army captain who served as West's principal in the past, is responsible for school climate. Ernestine Caldwell now handles academic affairs.

Wright is "a tough disciplinarian, and he knows the community," Vallas said.

Seeing classmates hauled away in handcuffs sends a message to would-be troublemakers, he said.

"Some students have to learn the hard way," Vallas said.

Vallas acknowledged there were no guarantees that the violence would end. Wright said last night he was optimistic that things would improve.

"We want to move forward. All these things are disrupting students' education," he said.

When they returned to the building after the evacuation, Wright gathered students into the auditorium and talked to them about the anger stemming from James' removal.

"We told them Mr. James is not that far away and told them that their education comes first, no matter what is going on in the district," Wright said. James has been reassigned to the headquarters for the Southwest Region of the district.

Wright said he had high hopes for the students.

"Monday, I expect my students to show up for school with a positive attitude," he said. "Kids don't want their academic future in jeopardy."

Many teachers were absent yesterday, Wright said, but he did speak to those in attendance. Wright said that some teachers were afraid and others tired of the media attention.

"I had a chance to thank them for what they've done," Wright said. "They want a good school environment."