Mayor Bloomberg led the way yesterday in naming 12 schools — 10 high and two middle schools — where criminal behavior by students is such a problem that it is disrupting learning. It was a risky move for the mayor and his schools chancellor, Joel Klein, to acknowledge there is a problem and risk further demoralizing the students and teachers in those dirty dozen schools, as there’s a chance the designation becomes self-fulfilling. Only time will tell if the mayor’s move was the right one. But all signs yesterday were encouraging. “If I have to put a police officer next to every kid, we’ll do it,” Mayor Bloomberg told reporters. “We are not going to tolerate disruptive behavior or criminal behavior.”

That’s the right message for the mayor to be sending under the circumstances. At the 12 schools in question — Evander Childs, Adlai Stevenson, and Christopher Columbus High Schools in the Bronx; South Shore, Canarsie, Thomas Jefferson, Sheepshead Bay, Franklin K. Lane High Schools in Brooklyn; Washington Irving High School in Manhattan, and Far Rockaway High School in Queens, as well as two Bronx middle schools, JHS-22 and IS-222 — the average number of major crimes last year was 19, and the average number of weapons was 17.6. This is not about students speaking out of turn in class; it is about violent, criminal behavior.

Messrs. Bloomberg and Klein say they plan to deal with this together with the police commissioner, Raymond Kelly, by doubling the number of police officers on duty at each of these schools, to 26 from about 13. It was a good sign, too, that yesterday’s announcement was made by Mr. Bloomberg together with the teachers’ and principals’ union leaders. On this issue, there’s no reason for labor and management to be at odds — a safe school for students is a safe workplace for union members.

Messrs. Kelly and Bloomberg have, these past two years, kept the crime rate down in the city as a whole. If they can extend their success to these troubled schools, the city will be even more grateful. It’s challenging enough to teach reading and writing in a monopoly government-run public school. A safe learning environment at least gives students and teachers a chance at success.