The boy, Jesse Lewis, had just seen his teacher shot and urged the others to flee while the gunman, Adam Lanza, put a new clip into his semi-automatic rifle.
"He yelled, 'Run!' Adam reloaded and shot him in the head," said Scarlett Lewis, who learned details of the events inside the classroom from investigators who gathered accounts from children who survived.
"When I heard he used his last few seconds on earth to try to save his friends, I was not surprised," she said. "I am so incredibly proud of him."
The boy's actions were first reported by The Hartford Courant.
Lanza shot his way into the school on Dec. 14 and killed 20 first-grade children and six women in one of the worst school shootings in U.S. history. He also killed his mother earlier in the day and committed suicide as police arrived at the school building.
A report on the Newtown shooting by investigators is due to be released soon. Investigators have not disclosed a possible motive for the massacre.
In Jesse's classroom, which was led by teacher Victoria Soto, 11 students survived, including some who ran past Lanza when he stopped to reload. In the classroom led by Lauren Rousseau, only one child survived. Both teachers were killed.
Scarlett Lewis said several people emerged as heroes that day, but her understanding is that some of the survivors ran because of what her son did to help them.
Lewis has dedicated herself recently to the Jesse Lewis Choose Love Foundation, which promotes ways for communities to "choose love over anger, gratitude over entitlement, and forgiveness and compassion over bitterness." The foundation was inspired by a message that Jesse had left on their kitchen chalkboard with the words "nurturing," ''healing" and love."
Earlier on HuffPost: