This decline, which began in 2012-13, has coincided with a decrease in suspensions and school-related arrests and summonses. The Police Department on Thursday released data on arrests and summonses from the second half of the 2015-16 school year. The department said there had been a 10 percent decrease in arrests and a 37 percent decrease in summonses issued by the school safety division from January to June of 2016, compared with the same period in 2015. The Education Department has previously said that the number of suspensions in public schools also declined in the first half of the 2015-16 school year, down 32 percent from the same period in 2014-15.

The number of weapons confiscated in the city’s public schools, however, has increased for the last two years to 2,053 this past school year from 1,347 in 2013-14.

Mr. Bratton argued the increase was “a positive thing” because it meant that school staff members and school safety agents were doing a better job of finding weapons before they could be used.

Within hours of the announcement, though, the charter school advocacy group Families for Excellent Schools sent out an email highlighting the increase in weapons recovered as evidence that undercuts Mr. Bratton’s claim that public schools were getting safer.

The group in recent months has repeatedly painted the public schools as increasingly dangerous. In April, the group and several public school families sued the city’s Education Department in federal court, claiming that it was depriving children of their right to an education free of violence and bullying. The lawsuit relied on state data showing a 23 percent increase in violent incidents in city schools from 2013-14 to 2014-15. The state data reflects a wider range of incidents than those that are tracked by the Police Department and has been widely criticized as misleading. On Monday the state Board of Regents proposed changes that would narrow the types of incidents that get reported to the state in the interest of clarity.