Sluggish cognitive tempo (SCT) symptoms are associated with social difficulties in children, though findings are mixed and many studies have used global measures of social impairment. The present study tested the hypothesis that SCT would be uniquely associated with aspects of social functioning characterized by withdrawal and isolation, whereas attention deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) symptoms would be uniquely associated with aspects of social functioning characterized by inappropriate responding in social situations and active peer exclusion. Participants were 158 children (70% boys) between 7-12 years of age being evaluated for possible ADHD. Both parents and teachers completed measures of SCT, ADHD, ODD, and internalizing (anxiety/depression) symptoms. Parents also completed ratings of social engagement and self-control. Teachers also completed measures assessing asociality and exclusion, as well as peer ignoring and dislike. In regression analyses controlling for demographic characteristics and other psychopathology symptoms, parent-reported SCT symptoms were significantly associated with lower social engagement (e.g., starting conversations, joining activities). Teacher-reported SCT symptoms were significantly associated with greater asociality/withdrawal and ratings of more frequent ignoring by peers, as well as greater exclusion. ODD symptoms and ADHD hyperactive-impulsive symptoms were more consistently associated with other aspects of social behavior, including peer exclusion, being disliked by peers, and poorer self-control during social situations. Findings provide the clearest evidence to date that the social difficulties associated with SCT are primarily due to withdrawal, isolation, and low initiative in social situations. Social skills training interventions may be effective for children displaying elevated SCT symptomatology.