Tue Dec 18, 2012 7:41pm EST (Reuters) - An elementary school in Newtown, Connecticut, was put on lockdown on Tuesday, the first day back at school for most of the town's children since a gunman killed 20 children and six adults in a shooting rampage at another grade school in town. As funerals continued for victims of last week's gun massacre at Sandy Hook Elementary School, local media reported that Head O'Meadow Elementary School was placed on lockdown for reasons that authorities declined to discuss. The lockdown came as educators and officials across the country grappled with how to respond to the shooting and wondered if there was any way to keep a rampaging gunman from breaching school grounds. Elsewhere, a phoned-in bomb threat forced the evacuation on Tuesday of more than 800 students and staff at a junior high school in the city of Idaho Falls in the eastern part of Idaho. Idaho Falls police, using a bomb-sniffing dog, uncovered no explosives at Taylorview Middle School during a two-hour search, but school district officials canceled classes for 750 seventh and eighth grade students and 85 faculty and staff members. "We're taking every incident involving schools very seriously and we plan to make any person who is threatening children accountable," police spokeswoman Joelyn Hansen said. News of the apparent hoax came one day after police in Boise, Idaho, took a man into custody outside an elementary school after receiving a report that he was suicidal and on his way to his child's school. And in Palm Springs, California, an 18-year-old man was arrested on Tuesday after allegedly posting a threat against Palm Springs High School using the Facebook account of a 15-year-old friend who attends the school, authorities said. David Guadalupe Torres, 18, was charged with making criminal threats, a felony, for posting a message on Monday night that threatened to shoot students at the school, police said in a statement. The threat was reported to police on Monday by the parents of the friend. When that student learned of the post and confronted Torres, he admitted writing it as a joke, police said. Torres was being held on a $75,000 bond. A search of his home did not recover any firearms, police said. Additional reporting by Barbara Goldberg and Laura Zuckerman; Writing by Dan Whitcomb; Editing by Cynthia Johnston and Eric Beech