Students returned to their classrooms in shattered Newtown, Connecticut, just four days after a gunman massacred 20 children at an elementary school.

"This is a day to start healing," Newtown High School's principal Charles Dumais said in an email to parents before six schools opened two hours later than usual, attended by police officers and psychological counsellors to help those traumatised by the killings.

In a blog entitled The Beginning, Mr Dumais added: "Our collective strength and resilience will serve as an example to the rest of the world. Be strong, Newtown."

As America's famous yellow school buses once more rolled through the town, where some 5400 children are in various schools, Sandy Hook Elementary was eerily silent, shut out of necessity as it remained a crime scene. it was there 20-year-old Adam Lanza gunned down the six and seven-years-olds and six of their teachers before turning a gun on himself.

Police have warned it could take months for them to finish their investigation, which was set back because Lanza smashed his computer's hard drive, preventing police from retrieving any data.

Outside the school, 26 Christmas trees representing each of the victims stood decorated with ornaments, stuffed animals and balloons in the school colours.

At Newtown High School, a group of three girls hugged each other in the car park before starting for the doorway.

Arriving students were greeted at the main entrance by school staff, one calling warmly: "Welcome back, guys." Uniformed police officers stood in the entrance and guarded the drive up from the street.

Nanci Wallenta, taking her friend's son to school, said she was not worried about security and determined to get back to normal.

She said: "It's an isolated incident. You can't go through life being afraid. You can't live in fear. ... We're a strong town."

Miguel, 16, on his way to Newtown High School, added: "There's going to be a lot of tears."

Newtown yesterday continued the process, begun on Monday, of burying the dead.

While politicians and the pro and anti- gun industry attempted to grapple with the future of Americans' constitutional right to bear arms, Newtown tried to ease the devastated community back to some semblance of normality.

In a sign of the nerves felt by the community, Head O'Meado elementary school was put on lockdown as a precautionary measure, according to a local police spokesman.

Funerals held yesterday included those of six-year-olds James Mattioli and Jessica Rekos.

Mourners at James's funeral at Saint Rose of Lima Church were told how the first-grader loved maths. His family described him as a "numbers guy" who came up with insights beyond his years to explain the relationship between numbers.

Meanwhile, Jessica was said to be wild about horses and had asked Santa for new cowgirl boots and a cowgirl hat.

"Jessica loved everything about horses," her parents, Rich and Krista Rekos, said. "She devoted her free time to watching horse movies, reading horse books, drawing horses and writing stories about horses."

The Rekoses described their daughter as "a creative, beautiful little girl who loved playing with her little brothers, Travis and Shane".

"We called her our little CEO [chief executive officer] for the way she carefully thought out and planned everything," they said. "We cannot imagine our life without her."

In a letter to US President Barack Obama, First Minister Alex Salmond said Scotland shares the sense of shock and deep sadness felt by the rest of the world at the shootings.