Beginning in January, students and staff at Pattonville High School will have to wear ID badges around their neck at all times.
Students already have to carry an ID badge on their person.
The change, which was announced to students Friday and to parents in a letter later in the day, came after Principal Joe Dobrinic said a 17 year-old former student was recently arrested at the school.
In the letter to parents, Dobrinic said the former student entered the building and claimed to be re-enrolling in class. When he instead roamed the building, Dobrinic said the teen was arrested.
"While no one was harmed or threatened as a result of this situation, it underscores how difficult it is without ID badges to readily identify who belongs and who doesn't in a building of nearly 2,000 students and adults," Dobrinic wrote.
The letter said the school would also work with the Maryland Heights Police School Resource Officer on enhanced school security measures for the building.