To claim a person as a dependent, they have several rules and tests to pass. The first is they have to be a U.S. Citizen, or resident alien. They cannot be claimed as a dependent on another return. They also have to be a "Qualifying Child, or Relative". Based on his age, I went to "Qualifying Relative", and there are 4 tests to pass. The tests are: 1) Not a 'Qualifying Child' (over 24 years old) 2) Relationship test (He is your son) 3) Gross income test (He must make less than $3,400 in Gross Income) 4) Support test (You, as the taxpayer, must have paid for more than 50% of his support) If you meet these tests, you can claim your Son as a Dependent on line 6c of the 1040a, or 1040 long form. (IRS pub 17, chapter 3, table 3-1)
What Jack means is, if he qualifies, you can claim your son as a dependent, weather he is working on your taxes or not.