Persuasion is an essential social skill. Yet its development and underpinnings are poorly understood. In 2 studies, a total of 167 children aged 3 to 12 years took theory of mind (ToM) tests and participated in unscripted, seminaturalistic persuasive conversations. Children were typically developing (TD) or had deafness or autism spectrum disorder (ASD). High-level, informationally rich persuasive arguments increased with age in all groups in both studies, as did ToM. In both studies, ToM scores predicted persuasion skill over and above age, language ability, and deafness/ASD status. In Study 1, TD 8-year-olds outperformed age-matched deaf and autistic children in ToM but only equaled them in persuasive skill. Study 2 employed more challenging persuasion tasks and revealed superior persuasion performance by school-aged TD children compared with same-aged children with deafness or ASD. Deaf and ASD groups did better on Study 1's straightforward persuasion tasks than on Study 2's more challenging ones, whereas TD children rose to the added challenge without their persuasion performance suffering.