Introduction: This paper compared the social-emotional and moral developmental characteristics of a boy with Williams syndrome and a typically developing girl. Method: The sample consisted of two eighth graders and their mothers. Participants were recruited using purposive criterion sampling. This qualitative study adopted a holistic multiple-case design because it compared the interrelated social-emotional and moral developmental characteristics of two different profiles of children. Findings: Data were collected using the Social-Emotional and Character Development Scale (SECDS), semi-structured interview questions, spontaneous conversations, and observations. The quantitative data were analyzed using descriptive analysis, while the qualitative data were analyzed using content analysis. The results show that the boy with Williams syndrome is more successful than his typically developing peer in making plans and helping others, but less successful in making eye contact, making friends, and following rules in the absence of authority. The typically developing girl has better internal control in following rules, behaving politely and respectfully, and exhibiting moral behaviors because she wants to. The findings show that both children have relatively developed social-emotional and moral characteristics. Discussion: The fact that the boy with Williams syndrome was more successful in expressing his wants and needs, planning and organizing, helping, maintaining communication with strangers, and choosing positive behaviors compared to his typically developing peer; behaving according to people's opinions, having approval anxiety, making decisions, self-regulation, following rules in the absence of authority, peer relations, adaptation, understanding people's feelings, and having difficulty in distinguishing good and bad intentions were in line with the literature. The fact that the typically developing girl exhibited more extreme social actions such as initiating communication; making eye contact for a long time; apologizing for misbehaviors; following rules with internal control and exhibiting positive behaviors provided different information from the literature. These results provide a new and different perspective to the results that children with Williams syndrome exhibit more social behaviors than their typically developing peers.