Among children with neurodevelopmental disorders, those with Autism Spectrum Disorder (ASD), Attention-Deficit Hyperactivity Disorder (ADHD), and Specific Learning Disorder (SLD) present with notable social impairment, heightened rates of social anxiety, and deficits in social cognition when compared to neurotypical peers. Because parent- and child-reports of social anxiety are frequently discrepant, conventional scientific wisdom dictates the inclusion of these separate reports when measuring symptoms and impairment. Social anxiety and social cognitive deficits are associated with poor functional outcomes, but research has minimally explored these constructs in youth with neurodevelopmental disorders. The present study examined the predictive weight of social anxiety and social cognitive impairment on adaptive functioning in a sample of 99 youth (ages: 7-17 years) with a diagnosis of ASD, ADHD, or SLD. Social cognition significantly predicted adaptive functioning impairments as well as clinician ratings of global functioning and clinical impairment. Parent and child ratings of social anxiety were significantly different; this discrepancy did not predict adaptive functioning, though it was predictive of clinician-rated impairment and approached significance in analyses of clinician-rated global functioning. These findings further clarify differential symptomatic paths to functional impairment in this population and inform mechanism-based treatment research addressing social impairment in youth with neurodevelopmental disorders.