Consider that the school is full of 11-18 year olds with access to weapons of mass destruction and it seems to me that the apparent safety of the place for the past 50 years is due to luck rather then anything inherent in system.

Perhaps luck is inherent in the system. The canon storyline does include a literal luck potion, so similar things are plausible. They also have and use a seer, and short-range time travel. The latter two could be used in ways that prevent deaths without a corresponding reduction in close calls.