John Matarese said Kevlar-lined backpacks surged in popularity after the Sandy Hook Elementary shooting in December 2012, when 26 people, including 20 children, were gunned down by 20-year-old Adam Lanza.
"Some parents' groups say this is going overboard, adding children would not be able to get to their backpacks in time to protect themselves from a school gunman, especially if the backpack was in their locker," Matarese wrote. "But other families feel any protection is better than none in our schools right now."
School security expert Kenneth Trump told CNN that bulletproof backpacks are too shallow of a solution to a complex problem.
"The first and best line of defense is a well-trained staff and student body," Trump said. "If you need a bulletproof backpack, don't you need a bulletproof front pack, headgear, and bulletproofing the rest of your body down to your toes?"