The three incidents took place within the space of a week, in Pennsylvania, Colorado and Wisconsin.
Five girls, aged between six and 13, were shot dead in a one-room Amish schoolhouse in rural Pennsylvania on Monday. The gunman, Charles Carl Roberts IV, lined his victims up against the blackboard, tied their feet together and then shot them execution-style one by one. He then shot himself.
In suicide notes, 32-year-old Roberts said that he was haunted by the death of his prematurely born daughter in 1997 and by memories of molesting two relatives 20 years ago.
The close-knit Amish community abhor violence and have been victimised for their refusal to join the army during major wars. Rebecca Smoker, an Amish mother of six, said of the shootings: "You sorrow because the innocence is gone. It's not going to be the same again ever."
The Pennsylvania incident followed the death of a 16-year-old girl at a high school 35 miles outside Denver, Colorado, on September 27.
Emily Keyes was shot in the head, as she fled Duane Morrison, who had held and sexually molested six girls. Morrison, 53, then turned the gun on himself. The attack evoked memories of the 1999 rampage at nearby Columbine high school, which left 15 dead.
Two days after the Colorado attack, 15-year-old Eric Hainstock brought two guns into his Wisconsin high school and killed his principal. Hainstock was subsequently arrested and charged with murder. He has told police that he was aggrieved by the principal's failure to deal with the pupils who had been bullying him.
British teachers have said that their pupils have been closely following news of the shootings, but do not appear to be worried for their own safety. George Lear, citizenship teacher at Oathall community college, in West Sussex, said: "It's something that's relevant to them. It affects pupils of their age. But our students look at it as happening in a far-away country. Knives are seen as more of a threat in the UK."
Nonetheless, he hopes to raise the subject in citizenship lessons. "We'd look at gun laws in different parts of the world," he said. "In this country, there just isn't a culture where people have guns, unless they're farmers, and the guns are legally owned."
Nina Gavin, acting head at Corpus Christi primary in Wolverhampton, intends to mention the shootings during school assembly.
"We will say prayers collectively for the people who were shot," she said.
"But the children don't think anyone is going to come into their school.
They feel very secure here."
Chris Keates, general secretary of the NASUWT teachers' union, hopes that teachers will feel similarly secure.
She said: "You're dealing with an extremely different culture in America, with the constitutional right to bear arms.
"But there's always potential for problems on the street to spill over into schools. Eternal vigilance is important."