@AJH4 just so there is no confusion, and your post suggests there is as there no test that combines income and school to determine a dependent.
There are two flavors of dependents - Qualifying Child and Qualifying Relative.
for the Qualifying Child, if he is a full time student, under the age of 24, lives with your at least half the year (and temporarily away at college still counts as living at home) and provides less than 50% of their own financial support, then he is your dependent. Note there is no income test.
For the Qualifying Relative, he can not be a Qualifying Child, he earns less than $5200, and you provide more than 50% of his financial support, he is your depedent. Whether in school, whether living with you are not tests for the Qualifying Relative who is your child.
