Events took place outside a high school in the Catalan city of Sabadell on February 26th.
The aggressor, as the video shows, repeatedly punched and kicked the other girl in her face and head for over a minute.
Classmates stood by without intervening, one of them filming the video which has caused controversy across Spain after being widely shared on social media sites.
The victim, who suffered numerous concussions, has filed a complaint at her local police station.
According to Catalan daily El Periodico, the aggressor posted the following message on her Facebook after the video went viral:
"I'm fed up of people sticking their noses in my business, I hit her because I had good reason to and she should get on her knees."
The attacker had recently been transferred from another school for similar reasons of misconduct.
She has since been suspended indefinitely.