Purpose: Internships are a common form of short-term employment for students seeking to demonstrate their value to employers and thereby improve their post-graduation career opportunities. As such, performance during the internship has been found to be positively related to post-graduation vocational outcomes. Yet, internships also serve a developmental purpose, wherein students' performance is expected to change over time. We extend previous research by taking into account this dynamism and examining the relative validity of interns' job performance trajectories compared to static indicators of interns' performance for predicting post-graduation vocational outcomes. Design/methodology/approach: We analyzed data from 465 engineering interns at a large Canadian university. Interns' performance was evaluated by supervisors at three intervals during their internships. Employment outcomes were assessed through a survey 6-12 months after graduation. Using latent growth modeling, we assessed the predictive validity of performance trajectories above initial, average and final performance evaluations. Findings: Performance trajectories positively predicted receiving a job offer from the host organization and post-graduation salaries. This effect was consistently observed in almost every instance, controlling for initial, average, and final performance evaluations. Originality/value: This study introduces the concept of performance trajectories as a critical predictor of internship success. Additionally, it contributes to the dynamic job performance literature by presenting evidence for the robustness of evaluators' preference for performance trajectories, even in a field setting where memory heuristics may dampen the predictive effect of trends. Practically, this study provides guidance for interns and intern-support staff seeking to optimize internship experiences for career benefits.