William James Sidis is born in New York City to Boris Sidis, a psychologist, and Sarah Mandelbaum Sidis, a physician. His parents, both intellectual immigrants from Ukraine, were committed to nurturing his intellectual development.

Sidis is raised in a stimulating environment designed to encourage learning. His parents eschew traditional schooling methods in favor of their own techniques, focusing on direct instruction and a rich intellectual atmosphere. He begins reading the New York Times at 18 months and learns multiple languages very early.

Sidis is enrolled in grammar school but quickly becomes bored and frustrated with the slow pace. His parents withdraw him after only a few months, concluding that the traditional system is not suitable for his abilities.

Sidis passes the Harvard entrance exam with remarkable scores, demonstrating an astonishing grasp of mathematics and other subjects far beyond his age. However, the university initially deems him too young to enroll.

For a year, Sidis receives additional tutelage from his parents to further prepare him for the rigors of Harvard. This period focuses on honing his existing skills and addressing any potential gaps in his knowledge.

At the age of 11, William James Sidis is formally admitted to Harvard University, becoming one of the youngest students ever to attend the prestigious institution. This event garners considerable media attention.