When Mayor Bill de Blasio announced the city would no longer suspend students in kindergarten through second grade, he reinvigorated a debate about his “restorative” approach to school discipline.

Many advocates cheered the policy shift as a move away from punitive measures that can set children as young as five on a collision course with the criminal justice system. Meanwhile, the city’s teachers union balked, arguing that eliminating a disciplinary tool before all educators have been trained in alternative methods will only lead to more disruption.

But the debate about what will happen if those suspensions are eliminated hinges, in part, on a basic question: What are the city’s five- through seven-year-olds being suspended for in the first place?

The answer, based on new data from the city Department of Education, offers some ammunition to both sides of the debate. Here’s what the numbers show:

Nearly a third of the 801 suspensions handed out to students in kindergarten through second grade this past school year were reportedly for incidents of violence or serious physical disruption. Those infractions included: reckless behavior with substantial risk of serious injury (115 suspensions); using force or inflicting serious injury to school safety agents or other school personnel (104 suspensions); and Category I weapons possession (22 suspensions), which includes everything from slingshots to guns.

The most common suspension is for an offense that used to be categorized as horseplay. “Altercation and/or physically aggressive behavior” is the technical name of the category, and 373 suspensions were issued for it last year, 47 percent of the 2015-16 total. Until the 2012-13 school year, the education department categorized this offense as “horseplay,” though the broadness of the label makes it hard to know how it is applied in practice.

Most suspensions come from a small number of schools. Just 263 out of the 839 district schools that serve students in kindergarten through second grade issued suspensions last year. And of those 263 schools, 40 percent (or about 105 schools) only suspended one student. That means roughly 19 percent of schools are responsible for 87 percent of all K-2 suspensions, reflecting a trend that also exists among schools that serve older students.

The percentage of young students who get suspended is tiny, and the number of suspensions is falling rapidly. Just 587 of the city’s youngest students were suspended this past year, or less than one-quarter of one percent of all students in those grades. The total number of suspensions issued to K-2 students is down 60 percent over the past four years, a decline that began during the Bloomberg administration. (Last year, the city required that principals get approval before suspending students in grades K-3.)

Some students are suspended repeatedly. Among students who got suspended last year, 26 percent received more than one suspension. The city did not provide demographic breakdowns for the data, such as race or disability status.

Taken together, the numbers may lend some credence to the teachers union’s argument that suspensions are a necessary tool to handle the most severe misbehavior, and that without systematic training, teachers won’t be able to effectively manage their classrooms.

“An ill-conceived ban, combined with a lack of oversight of the current system and no real plan to move forward, will perpetuate an environment of chaos and instability that can undermine the success of the classroom teacher and the achievement of every student in his or her class,” said Richard Mantell, vice president of the United Federation of Teachers, at a recent forum.

Neither the UFT nor the Council of School Supervisors and Administrators, which represents principals, commented directly on the new numbers. CSA Executive Vice President Mark Cannizzaro said that suspensions were already falling and the city should “let principals make decisions where appropriate.” Cannizzaro, along with other advocates, noted that schools may report identical incidents in different ways, making the aggregate numbers difficult to parse.

Teresa Ranieri, who has taught kindergarten and first grade for the past 11 years at P.S. 11 in the Bronx, echoed their concerns about the new policy. She said her school only uses suspensions after a series of other interventions, and when students are a danger to themselves or others. She said she wished there had been more discussion and training among teachers before the city announced the new policy.

“When you just ban all suspensions, my next question would be: If I have a child who’s acting out and I’m not getting cooperation from home at all — they don’t come to meetings, they don’t take the child to screenings — what’s my next step then?” Ranieri asked. “None of us have received that support yet.”

City officials stressed that the education department is investing $47 million annually, in part to provide training “to ensure [educators] have the supports they need to manage behavioral challenges.”

“We’re going to be training a lot more teachers — all our pre-K teachers went through special training on social-emotional [support],” schools Chancellor Carmen Fariña said in a recent interview. “Most of the principals I’ve spoken to are perfectly OK with the plan.”

One mother, who spoke on condition of anonymity, said she supports the suspension ban. She said her son, who has an individual learning plan for an emotional disturbance, was suspended six times in kindergarten, partly because the school was unable to manage his behavior, which included physical outbursts.

“The point of suspension is you’re showing the child and student the consequences of their behavior,” she said. “If you have a student who doesn’t understand those consequences, [a suspension] doesn’t help them.”

For their part, advocates who support the city’s shift away from suspensions said the new numbers offer evidence that punitive measures aren’t needed.

“When you look at these massive declines and the enormous number of schools who suspend no students at this age, it just reinforces to me that suspending kids in kindergarten through second grade is just unnecessary,” said Johanna Miller, advocacy director for the New York Civil Liberties Union.

Asked about the more serious infractions, including weapons possession, Miller said there are very few situations where removing a student is actually necessary for the safety of others. The discipline code, she added, allows educators to remove students from their classrooms without logging an official suspension.

“Nobody’s saying that a trained adult cannot take the child out of the classroom and manage their behavior,” Miller noted. “What we’re saying is they shouldn’t then spend days in a suspension room.”

Dawn Yuster, who directs Advocates for Children’s School Justice Project, largely echoed those arguments. She said the most serious infractions, including using force against a school safety agent, are often the result of student behavior that is misidentified or mismanaged from the start.

“This charge doesn’t happen in isolation,” said Yuster, whose organization has handled numerous complaints about school discipline from parents. It “signals that further training [is] needed for school staff to be able to better support students.”