I worked as a Student Assistant (Wissenschaftliche Hilfskrafte) for two years (19 hrs/week) at an institute of a reputed German University. I have received a work experience certificate (Arbeitzeugnis) and the performance rating does not reflect the amount of work I have done. I have been rated as just above average even though I have worked on plenty of projects and have been way better than other student assistants.
I have had some issues with my supervisor at times and I have faced rude unprofessional behaviour on multiple occasions. I'm sure this non work related issue is influencing the rating.
I have enough evidence to support the quality of my work and there are publications in which I have made significant contributions.
I would like to know if I'm legally allowed to further escalate the matter and talk to the institute head about a fair rating?