FORMER US HEADMASTER Bill Bond was all set, last Friday, to board the next flight from his Kentucky home to Colorado, where two days earlier an armed vagrant had killed a female student before committing suicide at a suburban secondary school, when news broke of another deadly school shooting, this time in Wisconsin. He switched travel plans at the last moment, heading north instead to the midwestern state, where a 15-year-old boy had just snapped and fatally shot his principal. Mr Bond is a roving emissary for the US headteachers' union, the National Association of Secondary School Principals. 'When you hear about a shooting, I'm usually on my way to an airport within hours,' he said. Mr Bond was on the scene, offering advice to shaken staff in the aftermath of the 1999 Columbine secondary school massacre in Colorado, America's deadliest school shooting in which 14 students - including the two gunmen - and a teacher lost their lives, and last year's tragedy at Minnesota's Red Lake secondary school, where Jeff Weise, 16, murdered his guardians then mowed down five of his classmates and two staff before turning the gun on himself. He understands better than most what survivors of the latest school shootings must be going through. Mr Bond was principal of Heath secondary school in West Paducah, Kentucky, when Michael Carneal, 14, gunned down three of his peers in 1997. There hasn't been enough of him to go around over the last week. On Monday, a delivery driver barricaded himself in an Amish school in Pennsylvania with 12 female students. He was armed with enough supplies to see him through a lengthy standoff. It never came to that. Bristling at the police encirclement after a teacher alerted authorities, Charles Carl Roberts IV, 32, opened fire, killing three girls outright and critically injuring several more before shooting himself as officers stormed the building. The Wisconsin rampage fits the all-too-familiar profile of US school shootings - a picked-on young male who raided relatives' gun cabinet to settle some scores. 'The student felt the world had persecuted him, so he bought a shotgun and pistol to school and said, 'I'm going to kill someone,'' Mr Bond said. Like other incidents, it's also a tale of heroism by courageous staff. Weston school principal John Klang overpowered and disarmed Eric Hainstock, despite sustaining wounds from which he later died, almost certainly averting further death. But the Colorado and Pennsylvania incidents represent an unsettling new turn for the phenomenon. Duane Morrison, 53, took six female students hostage at Platte Canyon secondary school in Bailey, Colorado, sexually assaulting them, before the siege's deadly denouement. In Pennsylvania, Roberts singled out female students and it has emerged that he told his wife he'd molested two young relatives decades earlier and was plagued by fantasies of molesting again. 'Having a male intruder from outside with the particular twist of focusing on young girls is very disturbing,' said Delbert Elliott, director of the University of Colorado's Centre for the Study and Prevention of Violence. Experts fear a copycat effect might have been at play, a pattern observed before in school shootings, which typically occur in clusters. 'We've come to learn that anytime there's a school shooting, not long after, you're going to have more,' said Larry Hill, security supervisor to Memphis' schools and president of America's National Association of School Safety and Law Enforcement Officers. Mr Bond said one high-profile incident let the genie out of the bottle. 'You get a very troubled person, thinking about suicide and hating the world. He sees the impact another guy had by dying and starts making plans.' Dr Elliott said the incident at West Nickel Mines Amish School in Pennsylvania brought it home that no US school was safe. The Pennsylvania carnage brought to seven the number of US school shooting deaths this school year, with term barely a month old for most pupils. Besides the latest attack, over the past five weeks alone a man shot dead a teacher in a Vermont primary school after searching in vain for his ex-girlfriend, a shooting spree by a Montreal college student left one dead, and Wisconsin authorities charged three pupils with conspiracy to mount a bomb attack on their school. The death toll from school shootings (including suicides) in 2005-06 was 19, compared with 26 and 29, respectively, in the preceding two years, the worst since Cleveland-based National School Safety and Security Services began tracking incidents in 1999-2000. Ken Trump, the group's president, said there had been an increase in school-associated violent deaths, non-fatal shootings and reports of aggressive behaviour over the last three to four years. In Memphis, Mr Hill said he had fielded calls from parents concerned for their children's safety in school. On Monday, rattled authorities locked down four Las Vegas schools amid reports that an armed student was at large. Later this month, the shootings issue will top the agenda of a school security summit, organised by the US education department, in Chicago. Many experts link them to America's unusually large gun ownership - 40 per cent of households, according to a 2005 Gallup poll - and permissive attitude to firearms. Dr Elliott said America was no more crime-prone than other industrialised nations, but 'the lethality [of incidents] is different because of guns'. But gun-control proposals face entrenched opinions. Echoing many Americans' views, Mr Hill said controls wouldn't keep guns from criminals, overlooking the fact that very few school shooters had prior criminal records. The National Rifle Association has controversially proposed arming teachers. The suggestion was greeted with derision in many quarters, but in 2003 Utah enacted legislation permitting teachers with licences to take weapons into school, citing the deterrent value. Another less obvious factor in the shootings may be the rural nature of much of American society. Mr Bond said he was struck by the Arcadian setting of the Wisconsin school. He noted that shootings had occurred overwhelmingly in rural or suburban schools, where, he suggested, pupils might be more vulnerable to feeling alienated if they didn't fit in with small, homogenous student populaces, unlike diverse urban schools that can offer niches for everyone. Mr Bond and other experts say that shootings, threats against schools, foiled pupil plots and malicious pranks or hoaxes tend to spike in spring around the April anniversary of Columbine and prime test-taking season, by which time the school year is also sufficiently advanced that cliques have formed, grievances are being nursed, and milder punishments for transgressions have been exhausted with staff invoking harsher sanctions that might set students off. Mr Hill said security officers patrolling corridors and metal detectors were long-standing fixtures at most US schools. Meanwhile many are tweaking security measures to combat the shooting threat specifically. Minnesota, Ohio and Michigan recently ordered their schools to perform 'lockdown' drills in preparation for possible shooting scenarios. Moreover, after Columbine, in which authorities were criticised for missing 'red flags', schools have stepped up vigilance of student remarks and writing to try to catch warning signs, often drawing criticism that they're being overzealous. In August, New York schools adopted a disciplinary code, holding students accountable for threats made online. In the Red Lake and Montreal shootings, authorities later traced ominous web postings to the assailants. Many schools have also implemented anti-bullying policies and set up bullying hotlines to forestall victims from taking matters into their own hands. But still, Dr Elliott said, many overlooked elementary precautions such as a single point of entry, offering clear line of sight for staff to monitor entrants. In Colorado, Morrison struck on a day when the school's security guard was absent. Meanwhile, the fate of Washington's Safe and Drug-Free Schools and Communities programme, from which schools apply for grants to beef up security, hangs in the balance after President George W. Bush called for its elimination as part of budget cuts in February. In June, The New York Times reported that a Columbine memorial was being scaled back after fund-raising proceeds fell short of expectations. Public consciousness of Columbine - eclipsed by 9/11 and events since - had faded, it noted. Recent events, garnering global attention, had brought the issue back to the forefront of concern, Dr Elliott said. 'What's happened has rekindled people's memories.'