Self-assessment is a widely explored topic in educational research. However, more research is needed on some of the self-assessment practices and their relationship with academic performance. This study aims to fill the research gap by analysing students' self-assessment training, what type of self-assessment processes they report, and how they use feedback when self-assessing. These were explored through interviews with 65 secondary education and 122 university students. Participants reported (1) to self-assess frequently, (2) to prefer different feedback sources with secondary education participants preferring learning materials over agents, (3) to use different self-assessment processes with higher education participants using more advanced strategies and a wider variety of criteria, (4) to enact different self-assessment processes depending on the task characteristics, and (5) there were differences between reported vs. performed self-assessment processes. Our results lead to more insight into the self-assessment experiences and emphasise the need to strengthen self-assessment practices in the classroom.