Classes resumed at Kennedy Middle School in Woburn after a reported stabbing Thursday morning prompted students to shelter in-place.
A fight that broke out just before 8 a.m. between two students escalated when one student slashed another with a knife, officials said.
Police said the 11-year-old assailant was taken into custody and a small knife was seized. The victim, a 12-year-old student, was taken to a hospital to be treated for superficial wounds.
The 11-year-old will face discipline from the school district and could face charges at Lowell Juvenile Court as the investigation continues.
In a joint statement, Mayor Scott Galvin, police Chief Robert Rufo and Superintendent of Schools Matthew Cowley said the incident was not random and there was no danger to the school:
"Due to the fact that this incident involves juveniles, there are certain things we cannot discuss under the law, but we have determined that this incident was not a random act and it appears to be an isolated incident.
Out of an abundance of caution, the school was placed in Shelter in Place mode during the initial investigation, but the school has returned to its normal schedule at this time.
The safety, security and well-being of the students and all members of the school community is our first priority. We have determined that there is no further danger to the school."