Classroom interaction experience is one of the main parts of students' learning lives. However, surprisingly little research has investigated students' perceptions of classroom interaction with different attendance policies across different class sizes in the higher education system. To elucidate the effects of class size and attendance policy on classroom interaction, we administered a survey to 1,304 undergraduates in Taiwan. The questionnaire consisted of six dimensions: classmate supportiveness, classmate pressure, teacher encouragement, teacher supportiveness, study preparedness and class participation. The results indicated that attendance policy and class size have an interaction effect only on the teacher trait. Students in a small class with a never-taking attendance policy feel more supported and encouraged by their teacher compared with those in larger classes with the same attendance policy. When class size is larger, students in classes employing an occasionally taken attendance policy feel more supported from their instructors than those in the never-check attendance policy class. Attendance policy doesn't influence the student or the classmate trait, but class size does. Larger classes lower classmate supportiveness, student preparedness, and class participation compared with smaller classes.