A growing interest exists in the measuring of social adaptive functioning in children with mild to borderline intellectual disabilities (MBID), but valid instruments to measure this construct are lacking. The aim of the present study was to develop such an instrument and to examine it on its discriminate validity. In 141 children aged 8–12 years a new test battery was examined in four groups either with MBID, behaviour problems or both, and typically developing peers. The results show that children with either MBID or behaviour problems or both show more hostile intent attributions, set more internal revenge goals, generate more aggressive and fewer assertive responses, feel more confident in inadequate responses en select fewer assertive responses, than their typically developing peers. Children with MBID are characterized by relying on earlier experiences in encoding information, a small response repertoire, positive evaluation of submissive but not assertive responses, and the selection of aggressive responses. In addition, they have more problems with perspective taking, problem recognition, interpretation in general, inhibition, working memory, and emotion recognition, than their typically developing peers. Further, children with MBID and behaviour problems have more difficulties in social information processing when the information in social situations is more complex. It is concluded that the tasks of the test battery can discriminate between groups, and after further development of the material, can be used to obtain information on the competencies and disabilities in social information processing and social cognitive skills, in order to be able to offer adequate treatment to these children.