Heather McLaren, 17, spotted the distressed woman and rushed to help her.
Heather, a sixth-year pupil at Eastwood High School, had seen an advert on TV about how to give CPR.
She later heard that her speedy actions had helped save the woman's life.
Heather said: "I just did it – I didn't think about it. When I got to the woman I couldn't feel a pulse and there was no-one else around.
"I remembered seeing the Vinnie Jones advert on TV so I thought I'd try it."
Heather was walking to school in Newton Mearns when the incident occurred.
She quickly realised it was very serious.
Heather – who was on her own – immediately called 999 then started performing CPR, which she continued to do until an ambulance arrived five minutes later.
A doctor took over from Heather at the scene before the woman was rushed to hospital.
Later that day Heather heard that the woman had suffered a heart attack, but that she was now stable and would recover.
Now Heather – who has applied to university to study nursing – has been presented with an award in recognition of her efforts by Councillor Elaine Green, East Renfrewshire Council's convener of education.
Councillor Green said: "What Heather did was absolutely phenomenal.
"That she was able to not only stay calm and raise the alarm, but also performed CPR on the elderly lady for five minutes, all while on her own, is fantastic."
Heather, who lives in Newton Mearns, was honoured at the council's Eastwood House.
Accepting her award, Heather added: "It feels pretty good to save a life – and it's nice to get this award for it."
Eastwood High head teacher Stuart Maxwell was also full of praise for his quick-thinking pupil.
He said: "Heather is a very mature and responsible girl. We're very proud of her."
The incident happened on the morning of Monday, December 17 in Fruin Avenue, Newton Mearns.