You seem to be under the misunderstanding that an employer *ever* needs to give you a raise. That is not true: unless you have a written employment contract requiring raises at certain times (e.g. yearly), an employer NEVER has to give you a raise, regardless of your years of service, quality of work, how many hours or how hard you work, etc. It is purely voluntary to provide a raise, and so an employer may refuse  to provide one for any reason, including that you are a student.