Students at the elementary school where a gunman massacred 26 children and teachers last month were returning to class for the first time Thursday in a new building adapted to look exactly like their old one.

Sandy Hook Elementary School in Newtown, Connecticut has been closed since the December 14 tragedy in which a 20-year-old local man shot 20 small children and six staff members before committing suicide.

On Wednesday, families were invited to inspect the new school in the nearby town of Monroe, where a disused facility has been prepared to resemble the old one, right down to the pictures on the walls and crayons on desks, ABC television reported.

In a message to parents on the school website, acting principal Donna Page, who replaces the slain school head Dawn Hochsprung, insisted "the facility is safe, secure and fully operational."

Page said parents would be allowed to stay in the school when it opens for classes Thursday, to provide reassurance to their children, many of whom witnessed to the bloodbath.

"We understand many parents may need to be near their children on their first day(s) of school and you will be welcome. That being said, we encourage students to take the bus to school in order to help them return to familiar routines as soon as possible," she wrote.

The shootings, in which Adam Lanza wielded a semi-automatic assault-style rifle, provoked a major national debate on gun control and a promise from President Barack Obama to back a bill outlawing military-type weapons.

The killer, Adam Lanza, was laid to rest over the weekend after his father, a tax executive, retrieved his body from the authorities last week, a family spokesman said.

Lanza's mother, whom he shot at their home just ahead of the school massacre, was buried in New Hampshire last month.