This seems quite unlikely.
Whether or not you receive an end-of-year bonus (‘13th month’) from your employer depends on the provisions of the collective labour agreement or your contract.
Generally such agreements state that you must have worked for your employer for a certain period of time (e.g. one year) before you are entitled to an end-of-year bonus. As a job student you will most likely not work long enough to meet this condition.
Will you be receiving a bonus anyway? Lucky you! Don’t forget, though, that the same contributions that are taken from your normal wages will be deducted from this bonus as well.