This study addressed the psychometric properties of the Children’s Social Skills Test (THAS-C). Results were divided into two parts. Initial studies investigated 257 children attending Grades 2 to 4 in public schools of two cities in the countryside of the state of São Paulo. Study 2 assessed 1381 children and adolescents aged 7 to 15 years from public and private schools in cities located in the countryside of the state of São Paulo. Infit and outfit indexes showed adequate fit for both items and people. A progression analysis using Rasch measurement model showed greater people’s ability in function of response categories. On the other hand, the outfit index suggested good fit in all categories. These data show relevance for the structure of three analysis categories. Few items showed DIF. Precision data obtained with these two methods showed satisfactory indexes. These data enable validity evidences based on the internal structure. Such findings may facilitate the assessment process and planning of interventions that are more focused on individual needs.