An advocacy group known for its opposition to Mayor Bill de Blasio’s education policies says the mayor misled the public when it trumpeted a drop in violence in New York City schools.

The criticism and an accompanying report mark a new tactic for the group, Families for Excellent Schools, and highlight de Blasio’s potential vulnerability on the issue of school safety. His administration has been mounting an effort to overhaul school discipline, urging schools to give out fewer suspensions and use alternative approaches.

In a report released Thursday, Families for Excellent Schools points to state data showing that violence in schools is increasing. Almost 16,000 violent crimes were reported in schools in 2015 — almost 3,000 more than the previous year — and the highest number of incidents since at least 2005, according to the report.

At the same time, city data — which is collected and submitted in a different way, and has long differed from the state’s numbers — show a decrease in the total number of safety incidents since last year and over the last decade.

City officials said that the state’s metric is deceiving because it not distinguish between minor interactions and severe altercations.

“This data is misleading; the total number of incidents at NYC public schools decreased nearly 8% last school year to historic lows, and crime, arrests and summonses are down across the board,” said Toya Holness, a spokeswoman for the education department.

State officials implied that the metric can be problematic, since schools report their own data, and said the education department has already convened a task force to revise the system. The group’s objective is to make it less complicated to report incidents and emphasize violent offenses, state officials said.

“The Department’s ultimate goal is to ensure that we are able to report the most accurate school safety data possible,” said Jonathan Burman, spokesman for the education department.

Even as de Blasio’s critics say his discipline-policy changes have made schools less safe, advocates have raised a different set of concerns. They support the shift to a less punitive approach to discipline, but say the city has done too little to help schools make the transition. On Wednesday, the group Educators 4 Excellence-New York held a demonstration at City Hall to call for more guidance counselors and de-escalation training for teachers.

De Blasio’s push for alternative discipline strategies is part of a national shift away from “zero tolerance” policies, which called for harsh penalties even for nonviolent infractions. Such policies have been shown to disproportionately affect students of color, while doing little to improve student behavior.

Last year, the city required principals to begin getting approval before suspending students for insubordination, and de Blasio convened a task force to make policy recommendations around school safety and discipline. The mayor’s budget for next school year includes funding for some schools to be trained in “restorative justice,” which pushes students to repair any harm their behaviors have caused.

As some schools are just beginning to make the switch to this new discipline approach, critics of the shift are looking for signs that it is backfiring. One student caught with seven bags of marijuana was given only a warning card, according to a recent New York Post article.

Families for Excellent Schools, which has previously been critical of the administration’s stance on charter schools and its “Renewal” school program, is now joining the fray.

But others said say their claim has little backing. Dawn Yuster, the social justice project director at Advocates for Children, said she has seen little evidence that de Blasio’s reforms hinder school safety.

“[The NYPD] are the last people that want to risk safety of anyone and they have been real supporters of trying to make change,” she said.