I have three in an elementary school in Cherry Creek Schools and every door is locked, including the front. Anyone visiting the school must ring a bell and be admitted by someone in the office. The doors can be opened from the inside, but its still safer than just allowing anyone entrance to the school. And everytime something like this has happened, police are involved and the school sends a notice to all the parents and the school district calls with an automated message to parents of the school and surrounding schools.

I am soooo steamed right now for what happened. Sorry if I'm ranting.