This study aims to determine the undesired student behaviors encountered in the classroom, the effects of these behaviors, and teachers' coping methods with them. A case study design, one of the qualitative research designs, was used in the study. This research was carried out with secondary school teachers working in the central district of Düzce. In this study, 14 teachers' views were captured through semi-structured interview questions. The data were analyzed by using descriptive content analysis method. The results revealed that undesired student behaviors were disturbing the peace of the lesson, not being prepared for the lesson, sleeping during the lesson, distraction, disrespectful behaviors, fighting with friends, not obeying the rules, coming late to class. It was also determined that the undesired behaviors decreased teacher's motivation; the ability of the teacher to teach effectively, made classroom management difficult, decreased the academic success of the students, and caused problems with the school administration. It was found that most of the teachers warned the students to cope with or prevent undesired behaviors, and if it did not work and the problem continued, they talked to the family. In the context of the results of the research, suggestions were made for researchers and practitioners.