A Bronx school was locked down yesterday after two gunmen who had shot a teen nearby darted into the building, sources said.

The attackers fled to PS 129 after shooting the victim in the buttocks just after 3 p.m. on East 178th Street near Mapes Avenue in the Belmont section. The two 16-year-old assailants, whom cops refused to identify, were caught shortly afterward.

The victim was at St. Barnabas Hospital in stable condition.

It wasn’t clear how long the school was locked down.