Over the last several decades, researchers have documented how impaired reasoning by adult offenders impeded the intelligent waiver of Miranda rights. Logically, it stands to reason that juveniles – who are developmentally less mature and have less life experience than their adult counterparts – would possess even greater impairment, thereby heightening their risk for invalid Miranda waivers. Juvenile Miranda research supports this notion; with some researchers finding that psychosocial maturity, among other factors, affect a juvenile’s understanding of their rights. Yet, relatively few studies have examined its relation to Miranda reasoning and decision-making. Thus, the current study investigated the specific role of maturity in juveniles’ Miranda comprehension and reasoning. Participants included 236 legally-involved juveniles recruited from either a juvenile detention center or a juvenile justice alternative education program. The effects of psychosocial maturity were examined on a variety of Miranda-related measures and assessed a broad range of Miranda abilities. It was found that, in general, immature juveniles performed more poorly on all Miranda measures as compared to their mature counterparts. However, the impact of maturity varied considerably depending on the ability. Specifically, maturity was most important in the context of Miranda reasoning. As a novel addition to the literature, the current study also investigated the effects of developmental timing on maturity (i.e., immaturity-delayed versus immaturity-expected) on Miranda abilities.