The upper secondary school for individuals with intellectual disability should prepare for an adult life as an active citizen with great self-determination and participation in democratic decision-making processes. The extent to which and in what way the schools work to prepare the students and develop their skills are likely of great importance for the students' adult life. The purpose of the study was to increase the knowledge of how students with intellectual disability in Sweden are prepared for adulthood, with special focus on self-determination. Case studies on three schools were carried out through observations of decision-making processes and interviews with students and staff. The main findings consist of three different approaches to self-determination for students with intellectual disability: 'Targeted and Conscious', 'Forward with Uncertainty' and 'Braking and Protecting'. Increased knowledge about, and analyses of, the processes that take place when young people with reduced decision-making capacity, due to intellectual disability, make decisions with the support of others are important. Implications underline the need to strengthen the awareness, knowledge and support of school staff when it comes to strengthening students' decision-making capacity. The students with intellectual disability need to be equipped for a society where they as adults will be surrounded by choices and expectations of making decisions.