Longitudinal predictors of internalizing and externalizing behaviors in autism: Examining relationships with ritualistic behavior and social diagnostic features.

Autistic youth commonly experience co-occurring mental health conditions. Core autism features have been linked to internalizing and externalizing symptoms, yet longitudinal pathways remain unclear. This study examined how ritualistic and social diagnostic features predict later internalizing and externalizing behaviors in school-age autistic children. Caregivers reported ritualistic behavior (PDDBI), social diagnostic features (SRS-2), and internalizing and externalizing behaviors (CASI-5; BASC-3) at two time points (baseline Mage = 8.50, SD = 1.62, range = 6.0-11.5; follow-up Mage = 12.67, SD = 1.79, range = 8.7-16.1). Children (n = 139) were 79.1% male (n = 110), 20.9% female (n = 29), 5% African American/Black (n = 7), 0.7% American Indian/Alaska Native (n = 1), 7.2% Asian (n = 10), 17.3% Mixed Race (n = 24), 1.4% Other (n = 2), 68.3% White (n = 95), 17.3% Hispanic/Latinx (n = 24), and 82.7% non-Hispanic/Latinx (n = 115). Ritualistic behavior and social diagnostic features were associated at baseline (r = .590). Baseline ritualistic behavior predicted later internalizing behaviors, while neither social diagnostic features nor ritualistic behavior predicted later externalizing behaviors. Findings underscore the importance of examining specific core autism features, particularly ritualistic behavior, as early indicators of internalizing and externalizing challenges across development.