Science has long known that adolescence is a time of becoming, but a large-scale analysis now offers a more precise map of that unfolding: the teenage mind does not mature as a single, unified whole. Working memory — the capacity to hold and manipulate information — arrives well before self-control, the harder-won ability to resist impulse in favor of longer purpose. These are not one system lagging behind itself, but two distinct systems on two distinct schedules, and recognizing that difference may change how we accompany young people through the years of their becoming.