Though city public schools are often dangerous places, the Philadelphia School District's zero-tolerance approach to discipline makes schools less safe and less effective at educating students, according to a report released Thursday.

District students are too often punished harshly for minor infractions, and suspensions, expulsions, and transfers to disciplinary school are overused, according to the study's authors, who represent groups long opposed to zero tolerance.

The study comes amid a national debate on how best to stem violence in public schools.

Researched and written by Youth United for Change, a local student organizing group; the Advancement Project, a Washington civil rights organization; and the Education Law Center in Philadelphia, the report says the policy too often targets black and Latino students.

Jim Freeman, an Advancement Project lawyer, said that Philadelphia has become an "outlier" for its zealous use of zero tolerance, a no-excuses policy that results in the long-term exclusion of students who violate school rules.

"The trend in districts similar to Philadelphia is away from zero tolerance," Freeman said in an interview. "The folks at the School District are actively promoting zero tolerance, and in many ways they seem to be getting more harsh, more severe in their disciplinary practices."

Responding to the report, the district stood behind its practices.

In a statement, spokeswoman Shana Kemp said the district was committed to continued improvement in its academics. "The safety of our students is key to making these gains," she said.

At a news conference touting the report, dozens of teenagers in red Youth United for Change T-shirts said schools feel like prisons and are too quick to criminalize students.

To make their point, they had public officials enter a City Hall conference room through metal detectors, spreading their arms for pat-downs.

"We feel violated," Ashley McKnight, a senior at Kensington Creative and Performing Arts High School, said in an interview.

Students - and the report - accused the district of overspending on school security and underinvesting in social services. The district's student-to-school safety personnel ratio is 310-1, and its student-to-school psychologist/social worker ratio is 1,657-1.

The report also details racial disparities. For the 2008-09 school year, black students had 35 suspensions per 100 students; Latino students, 23 per 100; white students, 14 per 100; and Asian students, 5 per 100.

Referencing a national study, the report says that the racial differences cannot be explained by differences in behavior.

Harsh punishments are appropriate for severe infractions, such as bringing a gun to school or assaulting a teacher, the authors say. But many district suspensions are for low-level misbehavior - being out of uniform, bringing a cell phone to class.

The findings are based on district data for the 2008-09 school year, when 32.4 percent of 46,350 suspensions were for disruption, 18 percent for fighting, and 8.7 percent for simple assault. Lesser categories include offensive language, 8.3 percent, and dress-code violations, 2.5 percent.

The result, the report says, is the "criminalization" of students. The district's heavy use of harsh penalties, they contend, adds to the dropout rate and diminishes the school's ability to educate students effectively.

Philadelphia's suspension rate exceeds that of the rest of the state - 28.3 suspensions per 100 students in Philadelphia, compared with 9.1 per 100 for the rest of Pennsylvania.

For several years, the district did not formally expel students. Superintendent Arlene Ackerman reinstated expulsions in 2008, saying harsh punishments were necessary for the most serious offenders.

But Ackerman has made conflicting statements on zero tolerance.

At times, she has advocated the use of school-based interventions to handle behavior problems, saying that harsh consequences be used only as a "last resort." At others, she has talked tough, saying that any "act of violence" should trigger a 10-day suspension and an expulsion hearing.

The report recommends a host of fixes, including reallocating some school security funding to pay for more social services; creating a public reporting system for school discipline data; and rewriting discipline policies.

It also calls for the state Legislature to withhold funding from districts that over-rely on suspensions, expulsions, and transfers to alternative school, or have racial disparities in the way they use discipline.

State Rep. Tony Payton (D., Phila.), one of the school and city officials who attended the news conference, called the trends highlighted in the report "disturbing."

"The numbers should disturb all of us," Payton said. "The School District can revise their policy tomorrow, next week, next month if it's a priority."