Jim McCann, the vice principal of St. Joseph’s Primary School, made his way through the hallways, pointing like a proud father to the colorful paper butterflies crafted by his students that hung from the ceiling.

He cheerfully greeted each child by name as he passed them. Then he stuck his head into a classroom, where the students addressed him in unison, “Good afternoon, Mr. McCann!”

The school is in the largely Catholic Falls Road area of west Belfast, which was engulfed for decades by the bloody sectarian struggle in Northern Ireland known as the Troubles. Outside, where multicolored fencing provides a bright backdrop to children playing soccer in the yard, gunfire once ricocheted, with army snipers perched on rooftops and armored vehicles rolling by.

But since peace took hold here 25 years ago, the neighborhood feels worlds away from that past. To Mr. McCann, 68, the transformation mirrors his own evolution.

The now-vice principal spent decades involved in the Irish Republican Army, or I.R.A., a paramilitary organization that used violence to try to end British rule in the region. He was convicted of attempted murder and spent nearly 18 years in prison.