The claim is not supported by the historical record. Einstein’s documented school results show very strong performance in mathematics, including top marks in algebra and geometry. The persistent myth appears to come from confusion about a failed entrance exam in other subjects and from later retellings, not from evidence that he flunked math in school.
Caveats
Do not confuse Einstein’s failed Zurich Polytechnic entrance exam with failing mathematics; he reportedly performed well in math and physics.
Primary school records outweigh viral anecdotes, motivational myths, blogs, and unsourced videos.
Some versions of the myth stem from grading-scale confusion, which can invert the meaning of his marks.