This research aims to examine the self-regulation of students with different achievement levels toward science learning based on Zimmerman's model including three phases: forethought, performance, and self-reflection. The research was conducted based on the case study from the qualitative research method. The study group consisted of 12 students who have different academic achievement levels and are studying at different levels of a middle school in Kayseri province, Turkey. The data of the research were collectedthrough semistructured interviews and analyzed using content analysis. It was determined that each phase of self-regulation was not compatible with academic achievement, and individual differences came to the fore in students' self-regulation. The authors concluded that a student's level in all subdimensions of self-regulation was not the same.They also found that not only academic achievement affected the subdimensions of self-regulation, but also individual factors and differences.