This paper examines how teachers expressing their political views influence students' opinion formation and discussions in classrooms regarding controversial issues. We used the methods of Journell (2011) and built on the scholarship of Hess and McAvoy (2015) and Iwasaki (2021). As a case study, we observed a junior high school social studies class and the teacher's approach to a lesson on lowering the age of candidacy in Japan, especially concerning how and if the teacher's personal opinions influenced the students. Teachers' political neutrality is a growing issue of concern in citizenship education. Some Japanese educators and education authorities argue that teachers should avoid expressing their personal views on controversial issues because of how it may impact students. However, we found that teachers' opinions may have a limited influence on student opinions, thus adding nuance and insight to the existing literature. Namely, the impact of teachers' expressing political opinions in a classroom should be considered with factors such as their choice of teaching materials and methods. [Note: The publication year (2021) shown on the PDF is incorrect. The correct publication year is 2023.]