Determined Leo Phillips tackled the Yorkshire Three Peaks challenge to raise cash in memory of his grandma.
Leo, whose gran died from cancer three years ago, decided to take on the 24-mile trek over Pen-y-Ghent, Ingleborough and Whernside to help Cancer Research.
The 12-year-old Kettlethorpe High School pupil collected around £420, including sponsorship of more than £100 from school staff.
Leo, who lives in Royston, said: “It was hard but I got through it. The worst peak was Whernside because it’s just so long.
“I felt like giving up on the last one (Ingleborough), because after I’d done two peaks my feet were stinging, but I carried on because I didn’t want to fail.
“After the challenge I was amazed that I’d done it. I didn’t feel amazed at first - I felt tired and relieved.”
Leo completed the trek in ten hours and 20 minutes.
He had already taken on two of the peaks on separate occasions as part of his training but it was the first time he had tackled Whernside - and the first time he took on all three at once.
His mum Judith Heppinstall said: “When Leo said he wanted to do this challenge, I really don’t think he knew how enormous a task it was.
“Before he knew it people were behind him and it was only when he attempted each mountain separately that it dawned on him how massive a challenge it was, how great the risk of wanting to give up was and how not only physical strength was needed but mental strength was too.
“I still am in awe of my son for doing this – not just for himself, but to raise money to help fight against cancer.
“Leo lost his grandma to cancer. He spent a lot of time with her before and after school when he was younger and loved and now misses her very much.
“I know cancer has impacted greatly on his life – I’m sure it has on so many others.
“I’m very proud of Leo. It’s something he should be proud of too.”