This research aims to reveal the subjective well-being levels of classroom teachers with the explanatory sequential design method of mixed method research. In the quantitative part of the study, the subjective well-being levels of the classroom teachers were analysed according to the variables of gender, age, region of employment, professional experience, educational status and grade level taught, and the qualitative part was designed with the phenomenology method and examined according to the sub-dimensions of school engagement and teaching efficacy. In the quantitative part of the study, there were 340 participants, and the Teacher Subjective Well-being Questionnaire was used, while in the qualitative part, 27 participants were included, and the subjective well-being level was examined according to the sub-dimensions of school engagement and teaching efficacy. While the subjective well-being levels of the participants did not differ significantly according to the variables of the region of employment, educational status and grade level taught, they differed significantly according to the variables of age and professional experience. In addition, the participants stated that the factors affecting school engagement were professional commitment, responsibility, working environment, being valued, being respected, belonging and conscience, respectively. The areas that positively affected their teaching efficacy were field and pedagogical knowledge, communication, technology and classroom management, respectively, and those that negatively affected their teaching efficacy were pedagogical knowledge, communication, classroom management and lesson planning.