Forty science students received training for 12 weeks on delivering effective presentations and using a tertiary-level English oral presentation scale comprising three subscales (Verbal Communication, Nonverbal Communication, and Content and Organization) measured by 18 items. For their final project, each student was given 10 to 12 min to present on 1 of the 5 compulsory science books for the module and was rated by the tutor, peers, and himself/herself. Many-facet Rasch measurement, correlation, and analysis of variance were performed to mine the data. The results show that the student raters, tutor, items, and rating scales achieved high psychometric quality, though a small number of assessments exhibited bias. Although all of the biased self-assessments were underestimations of presentation skills, the peer and tutor assessment bias had a mixed pattern. In addition, self-, peer, and tutor assessments had low to medium correlations on the subscales, and a significant difference was found between the assessments. Implications are discussed.