["European Journal of Education, Volume 61, Issue 2, June 2026. ", "\nABSTRACT\nThe Classroom Assessment Scoring System–Secondary (CLASS‐S) is a widely used observation instrument. However, it is important to gain knowledge whether the instrument is applicable in its specific context. This study investigates the applicability of the CLASS‐S in Norwegian upper secondary schools. The sample included 95 upper secondary school teachers and their classes from two counties and 12 different schools, including both academic and vocational track classrooms (1342 students). During one school year, the teachers video‐recorded their teaching seven times; these videos were scored by certified raters of the CLASS‐S. Given the nested data, two‐level models were tested. Results supported the original three‐factor structure of the CLASS‐S (emotional support, classroom organisation, and instructional support) when the instructional learning formats dimension was modelled exclusively at the between‐level. Reliability tests revealed good overall item, scale, and interrater reliability values. Some evidence was found between emotional support, classroom organisation, and instructional support, and study track and teacher characteristics. The current study supports the applicability of the CLASS‐S in upper secondary schools in Norway.\n"]