Debbie Stiff was shopping with her husband Gary when she got stuck in a sunken paving slab in Market Street.
She fell, but 15-year-old Sam Hubbard came to her aid as it began to rain.
Mrs Stiff said: "We were going back to the car from shopping when my wheelchair caught on a slab and it tipped me out.
"I landed on my left side, which is my paralysed side, and thank God for the cotton wool I'd bought my mum because I rolled onto my head and it protected me from hitting it.
"I was left with a large gash on my leg, though, and had to go to hospital.
"There was a young lad from Dartford Grammar School who offered his blazer to cover me over as it started raining. I wanted to show my appreciation to him."
Mrs Stiff, of Cherry Avenue, Swanley, did not have the boy's name so contacted the school, who told her they would try to find out who he was.
She said: "You usually only get to hear about the bad things youngsters do, and I just thought what this boy did should be recognised.
"He missed his bus for school so that he could stay with me until the ambulance arrived.
"He was really polite and a lovely lad. He told his friend to catch the bus, and he would stay with me.
"He took his jacket off and also helped my husband with all the shopping bags."
Sam was reunited with Mrs Stiff when she made a presentation to him during a school assembly.
He said: "I was just coming out of Dartford park and was about to get on the bus when I saw this lady fall out of her wheelchair.
"I ran over the road to go and help, and three of my mates turned up.
"I used my blazer to cover her feet where they were exposed to the elements.
"It was later revealed she had a two-inch gash on her leg.
"It was good to see her when she came back into the school and made a small presentation thanking me."
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