Yes if your provided more than half his support. If your son was away at college for four months, you can say he lived with you the whole year. The IRS considers being in school to be a "temporary absence."
Here are the requirements for claiming a child on your tax return:
- Relationship. Your child must be related to you;
- Age. Your child must be under age 19 or, if a full-time student, under age 24. There is no age limit if your child is permanently and totally disabled.
- Residency. Your child must live with you for more for more than half the year, not including temporary absences such as school, vacation, business, medical care, military service, or detention in a juvenile facility;
- Support. Your child did not provide more than half their own support;
- No one else is claiming them, such as the other parent, in cases of divorced parents.