This research aimed to use self-assessment In the reading
behavior of twelfth-grade students of SMA N 1 Toba. Specifically, the study characteristics are a case study. The subject of the research was the 20 students of Eleventh Grade Science 2. To obtain the data, the researcher used interviews and classroom observations. To process data researcher used Miles and Huberman's (Sugiyono, 2018: 134) activities in analyzing qualitative data. This research shows that the self-assessment used is metacognitive KWL (Know, Want, Leant). Students fill out the form to activate their prior knowledge; after that, they have a question for critical thinking, and then they summarize their learning. The interviews also revealed that students gave positive feedback in Response to self�assessment, which helps them take care of themselves. Based on the form students fill out, KWL (Know, Want, Learnt). Students have passive and active sides. Students can ask questions critically and respond well during feedback. Still, some passive students need questions related to the learning topic, become
listeners, and want to avoid being involved in the discussion. Furthermore, from the interview, it is found that the students give positive responses to self-assessment since it can help them maintain their reading behavior and motivate them to actively participate in the learning process, especially reading activities. Nevertheless, there are some negative responses from students who stated that
they were confused or did not know what exactly the function of self-assessment is. Based on the form students fill out, KWL (Know, Want, Learnt). Students have passive and active sides. Students can ask questions critically and respond well during feedback. Still, some passive students need questions related to the learning topic, become listeners, and want to avoid being involved in the discussion.

Keyword: Self-assessment, KWL (Know, Want, Learnt), reading behaviour