There were conflicting reports about whether the student fired the .32-caliber handgun at a teacher.
Lafourche Parish Sheriff Craig Webre said the suspect, believed to be 15, walked into an English class taught by a teacher he never had before, with the semiautomatic firearm, CBS affiliate WWL-TV in New Orleans.
According to Webre, the student pointed the gun at a whiteboard and pulled the trigger, but the shot never fired. He then pointed it at the teacher before targeting the ceiling, which he fired at, reports WWL.
The suspect, whose name was not released, then asked another student to follow him. When no one did, he left the classroom and went to the bathroom where he shot himself, Webre said.
The suspect was transferred to a second hospital, where he is listed in stable but critical conditions.
The Associated Press, citing Sgt. Lesley Peters, a spokeswoman for the Lafourche Parish Sheriff's Office, reported that the student did fire at the teacher before turning the gun on himself behind a stairwell.
Peters says the school about 45 miles southwest of New Orleans has been locked down. She says all other students have been accounted for.
The shooting is still under investigation.