You are expected to contribute toward the cost of your education through a Term Time Work Expectation. Although this isn't necessarily toward the cost of tuition. Books, school supplies, travel to and from home, and other personal expenses are considered part of the overall cost of attending Harvard College.
The important thing to understand is that earnings through a part time job do not have to be paid to Harvard or to the Financial Aid Office.
If you have an outside award it will first reduce your Term Time Work Expectation. For example it is typical for upperclassmen to have a work expectation of $3,500. If a student receives an outside award for $2,500 it will lower her/his work expectation to $1,000. If you are Federal Work Study eligible then this outside award will reduce your Work Study award.