If your son was still a Full Time Student in 2015 you should still be able to claim him even though he earned $10,000. See this article for more details on the dependent rules.
Here is the IRS definition of student
Student defined. To qualify as a student, your child must be, during some part of each of any 5 calendar months of the year:
A full-time student at a school that has a regular teaching staff, course of study, and a regularly enrolled student body at the school, or
A student taking a full-time, on-farm training course given by a school described in (1), or by a state, county, or local government agency.
The 5 calendar months do not have to be consecutive.
Full-time student. A full-time student is a student who is enrolled for the number of hours or courses the school considers to be full-time attendance.
Dependent children will generally be required to file if their earned income is
greater than $6,300 or their unearned income is greater than $1,050. See this
IRS Publication for more details on amounts.
If you do not claim your child as dependent he may file to receive a refund but is not required to if his only income is wages totaling less than $10,300
