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.

Each year, an estimated 318,000 defendants who do not comprehend the Miranda warnings waive their rights and provide incriminating evidence without the protection of counsel (Rogers, 2008), which make Miranda-related competencies one of the most pervasive pretrial issues. A wide range of issues could potentially affect an individual's capacity to provide a knowing and intelligent waiver. Previous Miranda research has focused narrowly on the effects of cognitive and developmental factors. The current study added to the Miranda literature by examining the impact of two highly prevalent conditions found in correctional populations, attention deficits and substance abuse. Adult defendants in custody (N = 118) were evaluated within 36 hours of arrest in order to assess both chronic psychological disorders and situational variables. Results indicate that attention deficits have a significant impact on defendants' ability to provide a knowing Miranda waiver, whereas substance use profoundly affected their reasoning about Miranda waiver decisions. This study represents the first systematic investigation of the effect of transient mental states on Miranda-related abilities with criminal defendants. Important implications for forensic practice are addressed.