The whole point of an attack on schools would be to spread terror. A multifaceted attack would do just that. Phase one would be to enter the schools. Securing the doors so that students would not easily escape. Load a fake police car and ambulance with explosives, arrive with first responders and detonate them. Attack police and first responders as they show up forcing a perimeter to be setup too far away for SWAT and SRTs to make an assault. Slowly and methodically kill everyone inside before burning the building down.
Nothing could be more terrifying. With the impotent putz we have in the Whitehouse, the thought of an attack within our bordes scares me to no end.
Do that to a half-dozen schools scattered around the country, and the next day and for the foreseeable future every school in the country would be deserted.
Furthermore, probably half the national workforce would be staying home with them.
THAT would have an adverse effect on commerce.