The attackers made teachers at Dan Maliki Primary School lie on the ground before shots rang out, a witness told Reuters.
No one claimed responsibility for the assault, but Islamist militant group Boko Haram - whose nickname means "Western education is sinful" in the northern Hausa language - has targeted schools before.
The movement has killed many hundreds in gun and bomb attacks since it launched an uprising against the government in 2009, opposing Western cultural influences and seeking to carve an Islamic state out of Africa's largest oil producer.
The gunmen hit the headteacher and three other teachers, leaving them severely wounded, said police spokesman Magaji Musa Majiya. Boko Haram was the main suspect, he added.
None of the pupils were harmed.
"They made the teachers lie down on the ground, then there were gunshot sounds and everyone scampered to safety," said Hauwa Jinjiri, a trader working on the school premises who witnessed the attack.
The shooting came a day after a rival Islamist movement Ansaru posted a video it said showed the bodies of seven foreign construction workers it killed after abducting them from a remote northern town last month.
Militants Islamists in northern Nigeria, most prominently Boko Haram, have become the main threat to the stability of Africa's most populous country and second biggest economy.
Boko Haram normally target security forces, politicians or Christian worshippers, although it has hit schools in the past.
Arsonists suspected of being Boko Haram members burned down seven schools in northeastern Nigeria's Borno state a year ago.
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