Basic motor competencies (in German: Motorische Basiskompetenzen; MOBAK) are performance dispositions empowering children to participate in the movement culture. For the diagnosis of basic motor competencies, a test instrument consisting of 15 test items for assessing third graders' basic motor competencies was developed (MOBAK-LUX-3) and validated empirically. Basic motor competencies were operationalized as test items in the form of basic motor qualifications, which are cultural tools formulated as a minimum standard. Data (MOBAK-LUX-3, age, gender, migration background, weight, height, sport club membership, weekly physical activity) were collected in 2015 amongst third-graders in elementary school in Luxembourg (N = 488; 50.4% female; M age = 8.8 years, SD = 0.51). A confirmatory factor analysis confirmed a four-factor structure ("locomotion", "object control", "moving in water", "object locomotion"; "CFI" = 0.94; "TLI" = 0.92; "RMSEA" = 0.036; "WRMR" = 0.89). Five classes with different competence profiles were determined through latent class analysis. The MOBAK-LUX-3 test instrument satisfies test theory requirements and can be used to determinate motor competence profiles.