The purpose of the present study was to develop a reliable and valid scale that assesses teachers' classroom leadership. Based on interviews with students and teachers and a review of literature, scale items were created for teachers' roles and responsibilities in leading students. Two independent samples participated in the study: 407 high school students during item generation and 594 high school students during scale validation. A principal component analysis revealed that the scale's 25 items contained four factors (i.e., interaction, motivation, in-class processes, and out-of-school processes) and explained over 54% of the total variability. Confirmatory factor analyses indicated acceptable fit and reliability coefficients were also found to be acceptable. It was concluded that the TCLS is a valid and reliable instrument in assessing teachers' classroom leadership. [Paper presented at the International Congress on Educational Administration (13th).]