This study investigated the effectiveness of self-, peer-, and teacher assessments in assessing EFL students' oral presentations. It also examined consistencies and differences among these three methods of assessment. Students' attitudes towards self-assessment and peer assessment were also investigated. This study is a mixed-methods sequential explanatory research in which both quantitative and qualitative data were collected. Using an adapted rating scale, 60 Iranian students in four advanced English courses were requested to assess their oral presentations and the oral presentations of their peers. Four teachers used the same rating scale to assess all students' oral presentations. To obtain students' attitudes towards self- and peer assessments, a questionnaire was administered before and after the employment of the rating scale. Students who revealed changes in their attitudes were also interviewed. Although the results showed no significant differences in the three assessment methods, the analysis of the mean scores revealed that teachers employed the strictest scoring criteria while peer assessors used the most lax ones. While the results of peer- and teacher assessments appeared to be consistent, no consistencies were discovered in self- and peer- assessments and in self- and teacher assessments. This study highlights that EFL students' involvement in assessing their own and peers' oral presentations can enhance their motivation to learn.