As social-networking sites attract younger followers, schools across the country are grappling with the fuzzy boundary between harmless online chatter and valid security concerns, reports the Dallas Morning News. The issue hit North Texas this month when two Frisco middle-schoolers were suspended for threatening to kill their teacher on Facebook. Legal experts say districts face an unprecedented challenge in this digital era: monitoring information without infringing on students’ free-speech rights. "Courts are still navigating how to deal with the internet and what happens on and off campus," said Mary-Rose Papandrea, an associate professor of law at Boston College who studies the effects of digital technology on student speech rights. "They generally say schools have the authority to restrict student speech off-campus when it’s materially disruptive to the school’s activity … or it advocates drug use or violence." But these online networks are becoming the modern equivalent of scribbled notes in class, making it unclear whether students are tossing offhand remarks or plotting real demolition…