Is he a first generation college student? Many schools have programs for first generation student to help them make the transition to college.
Schools tend to a lot of resources to help students. There are often writing centers, math centers, study skill workshops, tutors and office hours just to mention a few. The problem is that the student has to ask for help.
The decesion to drop a course has to start with why your son is struggling. Is he truely overloaded or is it a time management issue? Is he using the full resources available to him? Once you answer that then you can help him evaluate his options. A discussion with his advisor and his professor could also him him understand his options. Dropping a course should be the last option considered,