The school was set to hold a Mother's Day event when the armed robbery attempt occurred.
A footage that has been doing the rounds show the gunman Elivelton Neves Moreira, 21, pull a pistol on terrified families in Brazil as courageous Katia Sastre quickly stepped in.
Once she's sure he's down, Katya disarms him by kicking his gun away and grabbing it.
The criminal was rushed to hospital after Katia made an emergency call from her mobile but died from his injures soon after arrival.
Katia da Silva Sastre with Sao Paulo Gov. Marcio Franca.
He added of the mum-of-two: "Katia acted for two important reasons; in defence of society and in defence of her daughters, her family".
On Sunday, Sastre was commended in a ceremony by Sao Paulo governor Márcio França, who applauded her "dexterity, technique and courage" in dealing with the potentially very unsafe situation. "Her courage and precision saved mothers and children, yesterday at the door of a school", Franca wrote on Twitter.
The officer, who had gone to the event with her seven-year-old daughter, told colleagues: "I didn't know if he was going to shoot the kids or the mothers or the security guard at the school door".
Unbeknownst to him, 42-year-old police officer Katia da Silva Sastre was one of the women in the crowd.
"I just thought about defending the mums, the children, my own life and my daughters", Sastre said.
"She pushed the children out of the way and approached the thief".
It was during this moment that Katie, eased her own weapon out of a bag on her shoulder before opening fire on the criminal from close range. The governor of São Paulo Márcio França described the mother-of-two as "very brave" and her reaction to the gunman as "technically perfect" in a video uploaded on Facebook.