Good thing I took four years of martial arts. Stay in the class room. Go with the normal procedures. But I will stay closest to the door. Make sure I have a sharpened pencil. Then when he enters I impale his eye. Take his weapon(gun,knife,sword,coke bottle) and cripple his limbs with it. Making sure arrest is easy. Than I tape his mouth. We wait till cops come. If another guy walks in then I will have a better weapon. Rinse and repeat until safety arrives.