Student self-assessment is an important strategy to involve students into their own assessment process. This paper reports the results of a qualitative study designed to reveal how students know whether they have learned. The participants of the study were 168 high school students. A test comprising a scenario and open ended questions was used as the data collection tool. The answers from the students were analyzed using the content analysis method. Six distinct methods that students used to gather evidence to decide if they learned were identified. They are: self testing, getting help from others, summarizing, repeating, self questioning and explaining to her/himself. In addition, the reasons for using these methods were also revealed. The implications for improving students' self-assessment competencies and learning were also discussed at the end of the paper. (c) 2010 Elsevier Ltd. All rights reserved.