The attitudes and behaviors of teachers directly influence the cognitive, affective, and social development of students. These effects may be positive or negative and may last a long time. The aim of this study is to examine teacher behaviors and attitudes that can negatively or positively affect student progress. Using a qualitative research approach, the study adopted a basic interpretative research design. The study involved 229 undergraduate students studying at two state universities in Türkiye. Under the headings of positive and negative themes, participants explained the most influential teacher behaviors and attitudes they encountered in primary, secondary, or high school. A total of 183 positive and 187 negative narratives were analyzed. Positive teacher behaviors and attitudes were grouped under three categories: effective communication and ethical attitude, professional competence and dedication, and individual support and trust. Students have been found to be more confident, motivated, and satisfied with their learning, and are more likely to trust their teachers when they exhibit these behaviors. Negative behavior and attitudes were classified into discrimination and injustice, classroom management and communication problems, and occupational incompetence and irresponsibility. In addition to reducing students' motivation to learn, self-confidence, and respect for teachers, these negative behaviors impede their social development.