You can't claim a dependent for part of the year. Either he is your dependent or he isn't.
You can claim your son as a dependent if all of the following are true.
- He lived with you for more than half the year (or was temporarily away from your home while at school).
- He did not provide more than half of his own support for the year.
- He is not filing a joint tax return with his spouse (if he's married).
If he does not meet all these requirements, he might still be your dependent if his gross income for the year is less than $4,050.
(These criteria are specific to the information that you gave, and are not a complete list of the requirements for claiming someone as a dependent.)
Filing his own tax return, as long as it is not a joint return with a spouse, does not prevent you from claiming him as a dependent.
If he meets the requirements to be your dependent, he must indicate on his own tax return that someone else CAN claim him as a dependent, whether or not you actually claim him.
