PARIS—At a briefing for parents last week, the principal at a preschool in western Paris ran through the usual back-to-school checklist and scolded those bringing their children late. Then he turned to a new item on the agenda: “intrusion alert” drills to prepare teachers and children in case terrorists attempt to storm the school.

“The schools are targeted by terrorists,” said Olivier Rossignol, the principal, as a hush fell over the crowd of assembled parents. “We must train little by little so that the children can keep quiet and hide themselves in the classroom.”

As France prepares to mark the first anniversary of the Nov. 13 attacks in Paris, the new security procedures required at every school in the country are a sobering sign of how a spate of Islamist violence has changed everyday life.

The brutality of the assaults, usually directed at civilian targets, is forcing authorities to prepare for the possibility that even a preschool could fall into the crosshairs of Islamic State operatives or sympathizers.

The steady pace of terror attacks and foiled plots over the summer has cast a shadow over “la rentrée”—France’s annual back-to-school ritual. This month , a homemade bomb found near Notre Dame Cathedral the weekend after students returned to school rekindled fears about the terror threat.