Bruno Debattista, from Windmill Primary School in Oxford, brought a piece of shale rock containing what he thought might be a fossilised imprint to the after-school club at Oxford University's Museum of Natural History.
The museum experts were astonished to find that it appeared to contain the track-ways left by a horseshoe crab crawling up the muddy slopes of an ancient shore around 320 million years ago.
"Footprints of this age are incredibly rare and extremely hard to spot, so we were amazed when Bruno produced them at our After-School Club," said Chris Jarvis, education officer at the Museum and organiser of the Natural History After-School Club.
"Still more impressive is the fact that Bruno had a hunch they might be some kind of footprints, even though the specimen had some of our world expert geologists arguing about it over their microscopes!" Jarvis said in a statement.
The fossil has been confirmed by scientists as likely showing footprints of the pair laid down during the Carboniferous period, around 308-327 million years ago.
At this time, the sea was slowly being sealed off as Earth's landmasses crunched together to form Pangaea.
Bruno and his family have decided to donate the fossil specimen to the Museum's collection.