Background: Boredom is a common complaint among students. Boredom was previously found to be negatively associated with academic outcomes, such as academic motivation, strategies, and achievement. It is of interest to understand students' in-class boredom, especially factors that might exacerbate it. Aims: The current study examines the influence of teacher's boredom on students' in-class boredom and learning experience. It aims to understand the relationship between teacher boredom, students' perceived teacher boredom, student boredom, and student learning motivation. Sample: A total of 437 students (54.8% female, M [subscript Age] = 14.5 years, SD = 1.6) and 17 of their teachers (29.4% female, 76.5% 40 years old or below) participated in the study. Methods: We conducted an experience sampling study, in which participants completed a 2-week diary. Data were analysed using multilevel modelling. Results and Conclusions: Results from multilevel modelling of 2,675 post-class evaluations indicated that teacher boredom was negatively associated with students' motivation. However, the relationship between teacher boredom and students' perceived teacher boredom was not significant, suggesting that students did not accurately perceive whether their teacher was bored. Results from indirect effect analysis further revealed that students' perception of teacher boredom predicted student learning motivation through student boredom. In other words, perceiving teachers being bored promoted students' own feeling of boredom, which in turn reduced their learning motivation. Together, these results indicate that when a teacher is bored in class, or when students perceive that their teacher is bored, students would have lower learning motivation.