In more than 40 New York City public schools, long-term suspensions of students for disciplinary infractions are the norm, not the exception.

Since taking office in January, Mayor Bill de Blasio and his new schools chancellor, Carmen Fariña, have said that reducing the number of suspensions is near the top of their education agenda.

A New York World review of city data revealed that during the 2012-13 school year, at least 44 schools imposed long-term suspensions in at least 60 percent of all suspension cases. Citywide, about 20 percent of suspensions extend beyond five school days.

The long-term suspensions can last for weeks or even months. The impact of the discipline can last longer: Research has shown that suspended students fall behind in their studies and are more likely to drop out.

The city’s data are heavily redacted to protect the identity of individual students and does not indicate if a student had prior disciplinary actions preceding a long-term suspension.

The number of suspensions began to attract the attention of civil rights groups and elected officials after a dramatic rise in suspensions from 28,449 during the 2001-02 school year to 73,943 during the 2008-09 school year. The numbers have since fallen by 28 percent but elected officials, including de Blasio, have continued to call for reform.

In June 2013, then Public Advocate de Blasio sent a letter to Dennis Walcott, the chancellor at the time, calling for a review of the system’s suspension policies.“We need the capacity to manage minor outbursts and behavioral issues without taking children out of school for days at a time,” de Blasio said in the letter.

Some reforms have already been implemented. In 2012, after the City Council held public hearings and lobbied the Department of Education to alter the disciplinary code, the department restricted the use of long-term suspensions for students in kindergarten through third grade.

In a written response to questions from a World reporter, a DOE spokeswoman Marge Feinberg did not directly address the long-term suspension issue or the schools that rely heavily on them, but said, “Identifying alternatives that reduce the need for suspensions is a top priority for Chancellor Fariña.”

Long-term suspensions, termed “superintendent’s suspensions” by the DOE, can last from six days to an entire school year. These are the harshest penalty a principal can hand down to a student under the age of 17. Only students 17 and over can be expelled.

The city’s disciplinary code mandates long suspensions or expulsions only for the most serious infractions. Principals have a menu of options to handle less serious misdeeds, ranging from a parent conference to suspensions lasting up to five days.

The schools that rely heavily on superintendent’s suspensions are spread throughout the five boroughs, but the group as a whole contains a student population that is more heavily minority and poorer than the student population citywide.

These include I.S. 238 Susan B. Anthony Academy in Jamaica, Queens. Last year there were 66 superintendent’s suspensions at the school, and at least 88 percent of all their suspensions lasted more than five days. Of the 66 suspensions, 34 were for “physically aggressive behavior” that “creates a substantial risk of or results in minor injury.” The disciplinary code gives principals several options, ranging from a parent conference to a one-year suspension, to deal with this offense.

Meanwhile, P.S. 123 Mahalia Jackson, in central Harlem, gave out 46 superintendent’s suspensions, 72 percent of all of its suspensions. Again the majority of these superintendent’s suspensions were for “physically aggressive behavior.”

And the much-lauded Frederick Douglass Academy, which is known for its tough standards, gave out 32 superintendent’s suspensions last year, working out to at least 78 percent of the school’s total suspensions.

None of the schools responded to repeated requests for comment.

Tara Foster, an attorney for the Queens Legal Services, a nonprofit organization that provides free legal support to low-income residents, thinks that the disparities seen across the city’s schools are explained by differences in school culture.

“A lot of these are for lower-level infractions, where there is discretion,” said Foster. “Principals could do anything from a parent-teacher conference to a lower-level suspension, but we have seen that some schools like to jump immediately to the superintendent’s suspensions. The whole point of the discipline code is that it is meant to be progressive. You get this punishment, if the lower one didn’t work.”

Advocacy groups across the country have called for, and in some cases achieved, limits on the number of consecutive days a student may be suspended for a single incident.

In a report issued in June that cited studies linking suspensions to an increased risk of dropping out and involvement in the criminal justice system, the Council of State Governments Justice Center, a nonprofit organization that provides policymakers with research on public safety issues, called for a 10-day cap on the number of consecutive days a student may be suspended.

Washington state instituted a similar cap last year.

“Research on chronic absenteeism shows that missing that many days of school will cause you to fall behind and increase the chances you will repeat a grade or eventually drop out,” said Daniel Losen of the Civil Rights Project at the University of California, Los Angeles. “It goes without saying that the more days a kid misses because of a suspension, the more they will fall further behind.”

Michael Brickman, national policy director of the Thomas B. Fordham Institute, an education policy think tank, cautioned against completely taking these longer suspensions away from principals.

“Just requiring that schools reduce their suspension numbers doesn’t always result in a better school climate,” he said. “By doing that you may just be encouraging teachers to keep disruptive kids in classrooms. You have to balance the disruptive student’s education with not ruining it for everybody else.”

In New York, students who are suspended for long periods are assigned to one of 36 alternative learning centers. But Losen argues that these centers are not preventing suspended students from losing ground.

“In theory, if these were really great alternative programs, the way you could tell is that students returning to regular schools would be better than when they left,” said Losen. “We are just not seeing that.”