Children with Attention-Deficit/Hyperactivity Disorder (ADHD) are known to have difficulty with peer relations, though the mechanisms by which these children struggle with interpersonal relationships are not well known. The current study examined the relation between working memory (WM) and the encoding of nonverbal social cues using a dual-task paradigm tested in children with and without ADHD. Children and their parents were screened for the presence of ADHD or other exclusionary diagnoses, first through a phone screening and then through semi-structured diagnostic interview and rating scales. A total of 40 children were recruited (20 ADHD; 20 control) and were matched on age, sex, and IQ. Participants completed measures of intelligence, anxiety, sluggish cognitive tempo (SCT), and computerized tasks of social encoding and WM in both single- and dual-task conditions. Participant’s parents completed measures of psychological, behavioral, and social functioning in a separate room. A series of t-tests showed large between group differences on parent-reported externalizing problems, attention problems, social problems, and executive function. A series of repeated measures mixed-model ANOVAs revealed that both children with ADHD and control children performed significantly worse during the dual-task condition compared to the single task conditions. Also, children with ADHD had significantly lower performance than control children on task-based social encoding and WM. This study supports the role of WM in nonverbal social encoding in children, both with and without ADHD.