Previous studies of teacher enthusiasm have indicated that it can influence student motivation for learning, but it is not yet clear whether all students are influenced in this way, or only some of them. This study aimed to identify the percentage of students who were influenced by the teacher’s enthusiasm in normal classroom settings. Twenty-four grade 10 students were individually interviewed. The results indicated that all of the students had been influenced by the teacher’s enthusiasm, or lack of enthusiasm, in a recent lesson. Furthermore, the students described a wide range of teacher behaviors that they interpreted as indicating teacher enthusiasm. It was concluded that teacher enthusiasm is a motivational factor that can influence all or nearly all students.