I would be quite easy for a group of those teens to walk into a school with the students. Whether or not their tactics are sound is immaterial because the carnage they could inflict before being stopped would be massive. We all know those sub-humans are just looking to receive their perceived eternal reward so they freely accept death. The psychological damage of an attack on a school would be devastating.
Mentioned in a comment above "school, mall or movie theater near you!" All known to be target rich environments that are typically Gun Free Zones!