Emotions are an integral part of "classroom life" and are experienced in teacher-student interactions quite often (Hosotani & Imai-Matsumura, 2011). The present study focuses on teachers' emotions in classrooms. Its purpose is to establish which emotions are expressed by teachers in their interactions with students, the triggering situations of the two most frequent emotions, and their level of intensity and suitability. Teachers' emotions were observed by students of primary education during their practical experience work, in grades one to five. They used a scheme constructed for observing different aspects of emotions. The observations of 108 teachers in 93 primary schools from various Slovenian regions were gathered. The results show that primary school teachers express various pleasant and unpleasant emotions, with unpleasant emotions prevailing. The average frequency of teachers' emotion expression decreased from grade one to five. Anger was the most frequently expressed emotion (N = 261), followed by joy (N = 151). Teachers' anger and joy were triggered in different situations: anger predominantly when students lacked discipline and joy predominantly in situations of students' academic achievement. The intensity of expressed anger and joy was moderate in all five grades, while the assessed suitability of these two emotions was high.