"I didn't think we were going to live" ... teacher Kaitlin Roig.

"I didn't think we were going to live" ... teacher Kaitlin Roig.

As the world struggles to comprehend the reasons behind second deadliest school shooting massacre in US history, stories of heroism by class teachers are emerging.

The Daily Mail reports that music teacher Maryrose Kristopik saved 15 children during the shooting by barricading them into a closet, as gunman Adam Lanza was outside the door screaming "Let me in! Let me in!".

The paper quoted an unnamed mother, in her 40s, whose nine-year-old son was among the children, saying: "I want to thank her. She saved their lives."

Another parent, Brenda Lebinski, said her eight-year-old daughter was safe thanks to the "hero" teacher.

In the video above, Year 1 teacher Kaitlin Roig tells US television reporter Diane Sawyer how she hid her class in a bathroom to protect them from the gunfire.

"I just knew we had to get in there, I just kept telling them it's going to be OK," Ms Roig said as she fought back tears.

She recounted how she pulled a bookshelf in front of the door before closing herself and the children inside.

"I was so afraid that if he did come in and he would hear us he would just start shooting the door."

She said the children were extremely brave and she told them: "There are bad guys out there now; we have to wait for the good guys."

When the children became distressed she told them to "show me your smile". She told each of the children that she loved them "because I thought that was the last thing they were ever going to hear".

"I don't know if that's ok .. [for] teachers [to say that] .. but I wanted that to be one of the last things they heard, not the gunfire in the hallway."

Sadly, school Principal Dawn Lafferty Hochsprung was killed in the shooting at Sandy Hook elementary school, in Connecticut, along with at least five other staff members and up to 20 children.