Callum Leonard grabbed Jessica Wilde, 13, as she lay on the ground after they were attacked for no reason on a playing field. The friends had been chatting and texting friends when the man in his 20s set upon them.
Callum was hit so hard with the bar his skull was dented but he still managed to pull Jessica to her feet and run away.
Jessica suffered a long gash on her head. Police have now launched a hunt for the attacker who struck at 5.40pm on November 20 on a playing field near Wallbank Primary School in Tipton, Birmingham.
Callum's proud mum Claire Leonard said: "The first I knew, I got a phone call to say they had been attacked, but I didn't know how bad it was.
"They had managed to run away, and when I got to them they were waiting for the ambulance with Jessica's dad. "They had run for about 15 minutes before they stopped to ring anyone, they were that frightened.
"Callum's head was bleeding, and he'd got a 5cm cut on the front of his head, and a 4cm cut just above his ear. The blow has actually left a dent in his head.
"The man who attacked them never said anything to them, and although they were on their phones, he didn't seem interested in going after what they were carrying."
Jessica's mum Claire Wilde, from Coseley, West Midlands, descibed Callum as a 'little hero'.
said: "Jessica's got a 7cm cut on her head and grazes all over her scalp. She couldn't go horse-riding for two weeks afterwards and she's still not sure of going out.
"Before she would go out to friends' houses after school but now she's too scared. "They are both very lucky considering what could have happened. Callum is our little hero for what he did."
DC Gareth Homer, from West Midlands Police, said: "This was a completely random and brutal attack against two school children who were simply minding their own business.
"This could have been much worse and we have got to find the person responsible and bring him to justice.
"I believe the attacker was a white man, aged around 20. I would also appeal directly to the attacker to do the right thing and come forward to speak to us."