This study explored the consistency and difference of teacher-, student self- and peer-assessment in the context of Web-based portfolio assessment. Participants were 72 senior high school students enrolled in a computer application course. Through the assessment system, the students performed portfolio creation, inspection, self- and peer-assessment; three teachers reviewed portfolios and evaluated learning performances. There were significant differences in the results of the three assessment methods, among which teacher-raters adopted the most rigorous scoring standards, while peer-raters tended to use the most lax standards. The results of self- and teacher-assessment were discovered to be consistent; however, consistency was not discovered between self- and peer-assessment as well as peer- and teacher-assessment. In analyzing their consistency with the end-of-course examination, teacher- and self-assessment demonstrated high consistency, whereas peer-assessment showed a low level of consistency. (Contains 3 figures and 9 tables.)