The comforting claim that the century's greatest physicist flunked mathematics.
Documented
He mastered calculus as a teenager
Einstein excelled in mathematics from childhood, teaching himself calculus by his mid-teens. The myth traces partly to a confusing Swiss grading scale (1 was best, 6 worst; later reversed) and a 1935 Ripley's Believe It or Not item. Einstein himself laughed at the claim.
Assessment: Documented in school records and his own statements.
Stories
He did fail one entrance exam
At sixteen he failed the general admission exam for Zurich Polytechnic, but specifically its French, botany, and zoology sections, while scoring brilliantly in math and physics. He was admitted a year later.
Assessment: The grain of truth: he failed an exam, never mathematics.
Interesting claims
A story manufactured by the comfort industry
The claim: the failed-genius tale is deliberately cultivated, by motivational publishing, by schools, by anyone selling the idea that failure is the tax on greatness. Einstein is the poster because his face is free and his genius is undisputed. The myth is not about him; it is inventory.
Assessment: The story's spread through 20th-century self-help is documented, and its persistence despite easy refutation supports the comfort-theory reading. Whether anyone manufactured it is unprovable; that it is useful to everyone who repeats it is obvious.
Sources and further reading
Einstein's matura certificate, Kantonsschule Aarau, 1896, top grades in algebra and geometry (scale inverted in later retellings)
Ripley's Believe It or Not item, 1935, and Einstein's rebuttal as quoted in the press: he had mastered calculus before fifteen
Worth asking
Why do we need our geniuses to have failed first, and what does that need excuse in us?