In this article, I discussed about the way to train the student's ability of selfassessment in the lesson of Reading. The ability of self-assessment is important for student to determine the next goal of learning in his/her life. And the way to train the student's ability of self-assessment is also the way to become the agent of assessment. In this perspective, I considered (1) the relation to teacher's assessment and student's selfassessment, (2) the process that students participate in assessment and become the agent of assessment, (3) the rubric that proposed by Peter Afflerbach (2002), and the conference of portfolio that proposed by Beth Shipper & Joanne Rossi (1997). Thorough this study, I pointed out that (a) making out what the student achieved or what he/she should have done more is necessary, (b) for student, becoming the agent of assessment is to aim to relativize and reflect objectively self-assessment, (c) exposing the gap between student's self-assessment and teacher's assessment is important to train the ability of self-assessment effectively, and (d) thence training to the ability of self-assessment need the continual opportunity that teacher and student discuss about the gap.