He used the binder the way other kids used a diary. But where a diary confesses, his index categorized. Instead of “I felt sad today,” he’d write: “Event — Playground, 3:10 p.m. Stimulus: exclusion from game; Response: acute humiliation; Mitigation attempted: solitary swing; Outcome: introspective solution (invent game rules).” Reading it felt like watching a tiny machine reconfigure itself in real time.

The INDEX binder began innocently enough: a cover sheet, “For reference — Young Sheldon Cooper,” and an alphabetical table of contents. A: Allergies — none. B: Bedtimes — negotiable. C: Calculus — not yet, but practice problems included. Somewhere between G for Grandmother’s recipe for blackberry jam and P for Physics — experiments delineated with diagrams and safety warnings — the entries became less like study notes and more like map coordinates of the person he was becoming.

: Sheldon’s older brother, who later marries Mandy McAllister.

: Sheldon’s father and a high school football coach who struggles to understand his gifted son.