there are two tests for dependents.
Under the qualifying relative rules, your son qualifies as a dependent if he has less than $4700 of taxable income and you paid more than half his support. It doesn't matter if he is a student or where he lives.
Under the qualifying child rules, your son must be a full time student under age 24, and live with you more than half the year. Full time student in this case means attended school full time (as defined by the school) for part of at least 5 different months. So usually, attending college for one semester with a full time course load counts as being a "full time student" for the dependent test, even if the person was not in school the rest of the year.
For the "lived with you half the year" test, the child is considered to live with you even while they are away for a temporary absence. Being away at college is usually considered a temporary absence because the child still "lives at home" (their stuff is still at home, they return home for school breaks, they may intend to return home after graduation.) It is certainly possible for a student to establish a new permanent home that is not with their parents, and this depends on the facts and circumstances. If your child lives in an apartment with 5 other students, you pay the rent, and they come home for summer, they still probably live at home since the apartment is not much different than a dorm. If the student gets their own apartment with a spouse or partner, and takes other steps to make it their new permanent home (collecting their summer or winter clothing, furniture and other significant personal items) then they may have moved out and no longer "live at home" -- then you have to look at the dates to see whether the lived at home or could be considered to live at home for more or less than half the year.
