Tesis (Profesor de Inglés para la Enseñanza Básica y Media y al grado académico de Licenciado en Educación)In the Chilean context, English teachers are commanded to perform one hundred percent English classes, but unfortunately, this is not accomplished in every context; hence, this study decided to explore and compare teachers’ and students’ perspectives regarding the use of L1 in the EFL Chilean high school classroom. A quantitative instrument was applied to a total population of 510 being both teachers and students from different districts of Santiago. The results obtained in this study portrayed that both teachers and students agreed on the L1 usage under different situations, these ranging from grammar explanation lessons to managing discipline
