The study examines the factors that cause school absenteeism and how the high school/upper secondary can work to prevent school absenteeism and promote school attendance. The overall purpose of the study was to investigate what the high school/upper secondary school students describe as absenteeism prevention and promote attendance. The theoretical framework for the study consists of a socio-cultural perspective, a relational perspective, and the theory of KASAM. The study approach is qualitative and the study data were collected through mixed methods where semi-structured interviews were supplemented with a survey of the high school/upper secondary school students in grades 2 and 3. Based on the students' descriptions, the school's work on preventing absence and promoting attendance can be seen as complex. The students show, as in previous research, that many different factors influence the students' attendance and absence and that the causal factors can vary from student to student. The result further shows that there are a variety of factors related to the school's learning environments that can prevent absenteeism and promote attendance. The conclusion of the study highlights the importance of high school/upper secondary school working to strengthen students' motivation, participation, security, health, wellness and well-being. Highschool/upper secondary school should also work actively to ensure that the learning environment in the school is varied and that the teaching is adapted to the diversity of pupils' needs and conditions. Based on the results, it is determined that a broad repertoire of strategies and methods is needed in the school's absence prevention and attendance promotion work. The special pedagogical relevance of the study is made visible by the study showing that the school's attendance promotion and absence prevention work is strengthened by the school working to identify and map obstacles and opportunities in the school's educational, social and physical learning environments and based on the development of the school's learning environments at both individual and organizational levels.