He shouldn’t retake the AP Lang exam. His college intro composition or seminar (different names depending on the college) will be NOTHING like AP Lang. That class is just the default assumed background for Plan II, Harvard, Yale, Grinnell (etc.) Freshman English, not a replicate.
For that reason, most “elite” colleges don’t give credit for many AP courses. Some use AP for placement.
He/you could read Harlan Cohen’s_The Naked Roommate_ - real freshman questions, good intro to college.
Private universities will have tons of resources that public universities (even UT) don’t have - for instance, enough to support rent for a summer internship in a city for the child of a middle class family. Lots of support for kids who “don’t know what they don’t know”. There will also be more wealthy kids.
With UT Plan II/McCombs as his sure thing, he’s right to be shooting high. No regrets. 
