Additional Pay is for payments that are in addition to the employee’s base salary (e.g., stipends, bonuses). If the work-study student is owed additional hours that have not been paid to them, then this would not be the appropriate form to use and the hours should be submitted via the Off-Cycle/Final Pay form instead.
If the work-study student is owed additional pay for an action that is separate from their regular hours/salary (e.g., if the student has been given a STAR award), then this would be the appropriate form to use.