Although teachers need to assess computational thinking (CT) for computer science education in K-12, it is not easy for them to evaluate students' programs based on the perspective. The purpose of this study was to investigate students' CT skills reflected in their Scratch programs. The context of the study was a middle school coding club where seven students voluntarily participated in a five-week coding activity. A total of eleven Scratch programs were analyzed in two aspects: problem decomposition and program development. Results revealed that students demonstrated proper decompositions of problems, which supported program development processes. However, in some cases, students failed to decompose necessary parts as their projects got sophisticated, which resulted in the failure or errors of programs. Regarding program development, algorythmic thinking had been identified as the area to be improved. Debugging and evaluation of programs were the necessary process students needed to practice. Implications for teaching CT skills were discussed.