Objectives <p>Neurodevelopmental disorders have significant public health impacts, and novel approaches to understanding these disorders are greatly needed. Social connectedness, including relationships with parents and peers as well as family and school environments, may serve as a protective factor for neurodivergent youth. Neural networks that support social processing could also influence outcomes for these individuals.</p> Methods <p>The current study used data from the large Adolescent Brain Cognitive Development^SM (ABCD) Study (<i>N</i> = 11,878) to explore associations between social connectedness, brain functional connectivity, and subjective and objective measures of neurodevelopmental functioning in youth. Linear mixed effects models assessed links between social connectedness and neurodevelopmental functioning. Mediation models evaluated whether connectivity of the salience network mediated these associations.</p> Results <p>Authoritative parenting practices and involvement in extracurricular activities were linked to better neurodevelopmental functioning (<i>p</i>s ≤ 0.002), while family conflict was associated with worse functioning (<i>p</i>s ≤ 0.003). Salience network connectivity showed no significant associations with either social connectedness or neurodevelopmental functioning (<i>p</i>s &gt; 0.01).</p> Conclusions <p>Although the sizes of the observed effects were small, our findings imply that fostering positive family relationships and encouraging extracurricular involvement may relate to improved outcomes for neurodivergent youth. Future work is needed to identify additional factors that influence neurodevelopmental functioning over time and to determine the neural mechanisms underlying these relationships.</p>