Did Los Angeles overreact to school threat?

This morning, as I was getting my younger son ready to go to school, my phone rang with an automated announcement. School was canceled, the recording said. Not because of snow or rain -- this is Los Angeles, after all -- but because a "credible threat of violence" had been issued against the Los Angeles Unified School District. As a result, almost 700,000 students, 45,000 teachers and 38,500 other staff members in the nation's second-largest public school system would unexpectedly be staying at home.