At 11 a.m. today, all Broward County's schools went on lockdown due to a "credible threat" received by Pembroke Pines police. An as-yet-unidentified informant reportedly said that "something big" was going to happen at Broward government buildings, which include schools. (And one "virtual" school!) Presumably, "something big" is also "something bad."
"Lockdown," according to a Broward Sheriff's Office official, means "no one in" and "no one out." Obviously, the Pembroke police have more information on the situation than we do, and we will have to trust their judgment. But intuitively, it seems like sequestering everyone in homeroom for the day has the net effect of turning moving targets into immobile ones. Doesn't it?
Update: The lockdown has been lifted after Pembroke Pines police declared the likelihood of a threat "diminished." Students may now return to their regular level of freaked out.