Purpose:
To investigate the content and criterion validity, and reliability of longitudinal clinical assessment of undergraduate dental student clinical competence by determining patterns of clinical performance and comparing them with validated standalone undergraduate examinations.

Methods:
Group-based trajectory models tracking students' clinical performance over time were produced from LIFTUPP© data for three dental student cohorts (2017–19; n = 235) using threshold models based on the Bayesian information criterion. Content validity was investigated using LIFTUPP© performance indicator 4 as the threshold for competence. Criterion validity was investigated using performance indicator 5 to create distinct trajectories of performance before linking and cross-tabulating trajectory group memberships with a ‘top 20%’ performance in the final Bachelor of Dental Surgery (BDS) examinations. Reliability was calculated using Cronbach's alpha.

Results:
Threshold 4 models showed all students followed a single upward trajectory in all three cohorts, showing clear progression in competence over three clinical BDS years. A threshold 5 model produced two distinct trajectories, and in each cohort a ‘better performing’ trajectory was identified. Students allocated to the ‘better performing’ trajectories scored higher on average in the final examinations for cohort 2 (29% vs 18% (BDS4); 33% vs. 15% (BDS5)) and cohort 3 (19% vs. 16% (BDS4); 21% vs. 16% (BDS5)). Reliability for the undergraduate examinations was high for all three cohorts (≥0.8815) and did not change appreciably when longitudinal assessment was included.

Conclusions:
There is some evidence to support that longitudinal data have a degree of content and criterion validity for assessing the development of clinical competence in undergraduate dental students, which should increase confidence in decisions based on these data. The findings also provide a good foundation for subsequent research.