This preliminary study is the first in a series of studies aimed at improving the self-assessment of undergraduate translation and interpreting students. Self-assessment is crucial to developing self-directed learning skills and enabling formative assessment - key components of lifelong learning competence. The study looks at the consecutive interpreting performance of two cohorts: eight students (4-5 sessions) from Autumn 2023 and six students (3-4 sessions) from Spring 2024. The accuracy of the students' self-assessments was compared with the teachers' assessments. Three key findings emerged: i) the correlation between student self-assessments and instructor ratings increased progressively from week 1 to week 4; ii) high-performing students' self-assessments were more closely aligned with instructor ratings; and iii) the greatest agreement between student and instructor ratings occurred when rating accuracy. This initial study sets the stage for future research to develop better teaching methods for self-assessment in translation and interpreting education. The findings suggest several implications for teaching, which are discussed along with plans for longer-term research.