Kahramanmaras province governor Mukerrem Unluer said a teacher and three students were killed in the latest attack. The attacker was also dead.
"A student came to school with guns that we believe belonged to his father in his backpack. He entered two classrooms and opened fire randomly, causing injuries and deaths," Unluer told reporters.
Four of the wounded were in serious condition and undergoing surgery, he said.
The attacker, an eighth-grade student, was the son of a former police officer, Unluer said, adding that the suspect was carrying five guns and seven magazines.
"We suspect he may have taken his father's weapons," the governor said.
Unluer said the attacker was also dead.
"He shot himself. It is not yet clear whether this was suicide or happened amid the chaos," he said.
Footage released by IHA private news agency showed a person, body and face covered, being evacuated in an ambulance, as well as tearful parents who had rushed to the school in the southern province's main city, Kahramanmaras.
Witnesses quoted by media said intense gunfire was heard.
Police increased security around the building, and television footage showed ambulances in the area.
'Will be held accountable'
Justice Minister Akin Gurlek said prosecutors had launched an immediate investigation into the shooting.
On Tuesday, an ex-student opened fire with a shotgun at his former high school in Siverek district of Sanliurfa province, wounding 16 people before killing himself in a showdown with police. Ten students were among the casualties.
Speaking to the ruling AKP party in parliament, President Recep Tayyip Erdogan promised that those found to have been negligent or at fault "will certainly be held accountable" over the school shootings.
Police detained one suspect after Tuesday's attack and suspended four officials from duty, Erdogan said. The school was ordered closed for four days.
School shootings in Turkiye had been rare until this week. In May 2024, a former student killed a private high school principal in Istanbul with a firearm five months after he was expelled.
Turkiye has strict gun laws that require licensing, registration, mental and criminal background checks, and severe penalties for illegal possession.