Last week’s tragedy in Newtown has schools across the nation on high alert. On Wednesday afternoon, Texas’s Crowley school district placed three of its schools on lock down after word of a potential security threat spread through social media and text messages. It had been a “precautionary measure” requested by the police, the district’s website said. Investigators found no credible threat, and an all-clear was issued later in the afternoon. Another school in Michigan was also placed on lock down Wednesday, after a photographer attempted to enter the school to report on school safety. Well done.