The stabbing occurred about 8 a.m., shortly after the school day started at John Adams High School.
The student, a minor, told police that five males attacked him.
South Bend Police Chief Scott Ruszkowski says several juveniles were in custody in connection with the incident.
The school was placed on lockdown for about three hours before it was lifted.
Principal James Seitz wrote in a letter to parents the incident “appears to be isolated” and that no other students were injured.
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