Columbus proved the Earth was round
The old claim turned out to be wrong and was rejected by evidence.
TaughtEducated Europeans in 1492 believed the Earth was flat and feared sailing off the edge. Columbus defied the flat-earthers and proved them wrong.
NowEvery educated European in 1492 already knew the Earth was a sphere, and had known for roughly eighteen centuries. The argument against Columbus was that he had the planet's size badly wrong, and his critics were right.
What actually happened
Eratosthenes measured the circumference of the Earth around 240 BCE and got within a few percent. Ptolemy's Almagest, Bede, Aquinas, and Dante all treat a spherical Earth as settled. The medieval symbol of royal authority was literally a globe held in the hand. There was no flat-earth establishment for Columbus to defeat.
The myth was largely manufactured in the nineteenth century. Washington Irving's 1828 romance about Columbus invented the dramatic scene of the flat-earth clerics at Salamanca, and later writers promoting a story of science-versus-religion adopted it. Jeffrey Burton Russell's 1991 book "Inventing the Flat Earth" traced the whole chain and is what pushed the correction into mainstream teaching.
The real dispute at Salamanca was arithmetic. Columbus lowballed the Earth's circumference and inflated the eastward extent of Asia, concluding Japan lay about 2,400 miles west of the Canaries. His examiners used better numbers and said the voyage was far too long to survive. They were correct on the geography. Columbus survived only because an unexpected continent was in the way.
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Who was taught this
Still standard through 2005, so anyone who finished school between 1950 and 1991 learned the earlier version.