A supervisor at Joseph Lakanal college disarmed the 14-year-old before police arrived, Aubagne mayor Jean-Pierre Squillari told reporters.
Both victims were hospitalised but neither suffered life-threatening injuries, he added.
There was no immediate indication that the shooting was linked to a three-week wave of protests, some violent, that have rocked high schools across the country.
President Emmanuel Macron condemned those incidents of violence on Monday.
BFM TV said the 14-year-old pupil had entered the school with the rifle hidden in a guitar case.
He was later detained by police.
"It's a kid who goes to that school. He entered with a rifle, the investigation will determine how, and fired twice in a corridor toward the principal and a teacher," Squillari said.
One student told Reuters that her maths teacher had played down the bang of the first gunshot blast as noise from nearby construction works.
A subsequent blast was followed by an alarm and classes emptied into the corridors.
"We were panicking, we ran," the student said.
"There were two ways out: one passage to the sports hall and one passage to go outside. Survival instinct took over and I ran towards the outside."
Opposition National Rally party leader Marine Le Pen, frontrunner in the race to replace Macron, said the government was losing control of security in schools.
"Schools, which should be sanctuaries, are now places where people risk their lives. Insecurity has entered the school. Many pupils and teachers go there with a knot in their stomach."
Macron's education and interior ministers are due to travel to the college later on Monday.
Eddy Sid, spokesman for the SGP-FO police union, told BFM TV there was no apparent link between the shooting and high school protests against understaffing and lack of funding for schools.
There had been no blockades at the Joseph Lakanal college, he added.
