Performance in and perceptions of computational thinking (CT) are considered vital dimensions for comprehensively assessing CT skills of students. In this study, secondary school students' CT performance and their perceptions were examined in terms of certain variables including gender, grade level, achievement and self-efficacy. Casual-comparative and correlational methods were used. The sample of the study consisted of a total of 328 fifth- and sixth-grade (10-12 years old) secondary school students taking visual programming lessons. CT performance and perception tests were employed as data collection tools. The results show that CT performance of boys was higher than that of girls. A significant difference was found in both CT performance and perception depending on grades. The results show that achievement in math positively affected CT performance and perception. However, achievement in IT affected CT performance less than achievement in math. Implications are discussed in terms of theoretical insights, practices for improving CT skills in secondary schools and directions for further research.