There is no such thing as a part-year dependent. The qualifications to be claimed as a dependent look at the year as a whole.
If you can claim your son as a dependent, he MUST indicate on his own return that he can be claimed by someone else.
If you're not sure if your son qualifies as your dependent, you could post another question - giving his age, student status, number of months he lived with you, etc.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
