it is not exactly like this. But lets say 1/3 support comes from custodial parent, 1/3 comes from non-custodial parent through 529 plan, 1/3 comes from student part time job. Nobody actually supports 50%. so nobody can take the exemption. if the 1/3 from non custodial parent 529 plan can be considered student support, then at least the student can. Also I am dealing with 2017.