Twenty-first-century skills are considered to be critical to student development. The present study aimed to validate a scale that reflects 21st century skills in education. The participants were 982 students in the fourth, fifth, and sixth grades at two primary schools in a large city in Shandong, China, who were all asked to learn English in a flipped classroom. This 5-point Likert scale assessed students' collaboration, creation, self-regulation, interest, and engagement in English as a foreign language (EFL) flipped classrooms in China. Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were adopted in this study. The EFA results demonstrated that the scale contains five dimensions with good indicators. Good model fits derived from CFA supported the five-dimension structure. Further analysis revealed that there were positive correlations between this scale and the other two scales: the Learning Self-efficacy and Adolescent Student Burnout Inventory scales, indicating that convergent validity was achieved. These findings confirmed that this scale is a reliable and valid tool for measuring 21st century key skills in EFL flipped classroom in China and may supplement the limitations of traditional teaching evaluations. In future studies, researchers may extend its use in other disciplines by examining its reliability and validity.