Reuters could not independently verify details of the violence that took place on Friday in the village of Let Yet Kone in the central Sagaing region.
According to reports in the Mizzima and Irrawaddy news portals, army helicopters had opened fire on the school housed in a Buddhist monastery in the village.
Some children were killed on the spot by the shooting, while others died after troops entered the village, the reports said.
Two residents, who declined to be identified due to security worries, said by telephone the bodies were later transported by the military to a township 11 km (7 miles) away and buried.
Images posted on social media showed what appeared to be damage including bullet holes and blood stains at a school building.
In a statement, the military said the Kachin Independence Army, a rebel group, and the People’s Defence Force (PDF), an umbrella organization of armed guerrillas that the junta calls “terrorists,” had been hiding in the monastery and using the village to transport weapons in the area.
Security forces sent by helicopter had conducted “a surprise inspection” and were attacked by PDF and the KIA inside houses and the monastery, it said.
It said security forces had responded and said some villagers had been killed in the clash and that the wounded were taken to public hospitals for treatment. The statement accused the armed groups of using villagers as human shields and said that weapons including 16 handmade bombs had later been seized.
The NUG also called for the release of 20 students and teachers it said had been arrested following the air strikes.
Documented violent attacks on schools surged to about 190 in 2021 in Myanmar from 10 the year before, according to Save the Children, a non-governmental organization.
Use of schools as bases by both the military and armed groups also increased across the country, the organization said in a report this month, disrupting education and endangering children.