The Social Skills Improvement System-Teacher Rating Scale (SSIS-TRS) has been widely used to measure the social skills and behaviors of children and adolescents that are challenging. Studies examining the psychometric properties of the SSIS-TRS have been conducted, but the dimensional structure and item properties of the SSIS-TRS have not been extensively examined with samples of preschool-age children at risk for social-emotional and behavioral difficulties. This current study was designed to examine (a) the dimensional structure of the Social Skills scale and Problem Behaviors scale of the SSIS-TRS and (b) the item function of the SSIS-TRS using item response theory analyses with data collected from teachers of a sample of 469 preschool-age children at risk for social-emotional and behavioral difficulties. A four-dimensional structure (i.e., Cooperation, Empathy and Relationship, Engagement and Interaction, and Self-Control) and a three-dimensional structure (i.e., Aggression and Defiance, Disruptiveness and Stereotypy, and Withdrawal) were identified for the Social Skills and Problem Behaviors scales, respectively. Item parameters of the SSIS-TRS were estimated using the generalized partial credit model. Item information curves were plotted for individual items; behavior indicators providing higher information for measuring corresponding social skills and problem behaviors constructs were identified. The limitations and implications for the present study are discussed.