The same type of bullet was also found in February in the hallway of the school in Belleville.
Eleven students from north St. Louis are being treated for minor injuries.
About a half-dozen students have been hospitalized after a St. Louis school bus collided with a Metro bus.
35 batteries, weighing about 100 pounds each, were taken from First Student buses in late June.
Police in Collinsville are looking for suspects who stole batteries from nearly three dozen school buses.
The batteries weigh roughly 100 pounds and can be sold for $50 apiece at a recycling center.
Parents in St. Albans picked up a video camera and tailed the bus to prove the route was longer than state law allowed.
School district in Franklin County would benefit from bill now in Missouri legislature.
Sen. David Pearce, declared that the bill is dead for the session that ends Friday.
State education officials are looking at ways to make the most of the limited amount of money available to pay for student transportation.