A smaller LAC type school will have courses generally taught by professors rather than grad students or TAs. While some (many) of these may be people who speak with an accent, the likelihood is that they will have studied/lived in the US for a longer period than a grad student, and thus, their accent may be easier to understand. In some fields, such as STEM, which attract an international demographic, there is likely to be more diversity in language use/accent. (That being said, I have a friend who teaches in a small LAC and their department includes 50% instructors with accents, although all are sensitive to the issue and many deliberately use teaching techniques such as powerpoint to mitigate any misunderstandings.)
I’m sensitive to your son’s issue, since (with no diagnosis) I remember nothing from my Intro to Philosophy class except for Dr Huang’s delightfully relaxing voice. But let me recommend that in this PC world you find a way to phrase the concern in a way that will minimize the inevitable charges of bias that will inevitably be attached to the question.