Wesleyan is a reach in the sense that any school with a sub-20% acceptance rate is considered a reach for anyone simply because in that 80+% of students who are being rejected are many students just as qualified as those who have been accepted.
However, your son definitely has the credentials of the kind of student that Wesleyan is looking for. And I don’t think that it is shock & awe that they are looking for. His essay is important. It’s his opportunity to introduce himself to them. What they are looking for is authenticity and genuineness in an essay written in his own voice.
The fact that he is interested in environmental studies is a plus. Wesleyan has emphasized this as a priority since the 1990s. The fact that he is looking for a campus where students are collaborative and are highly engaged in academics is a plus. That’s what they are looking for! He should explain why this is important to him. I think that if he visited the campus so that he could write about how he could contribute to the campus culture, that would be a plus. For example, would he like to work on the campus’s student run farm? If he could begin to refine his ideas regarding a career of involvement with environmental issue so that he could write about it in his essay that would be a plus - particularly if he could explain how he might integrate his interests in sustainability with Wesleyan’s approach in their Bailey College of the Environment.
Wesleyan is not an impossible acceptance. It does not require a hook. They are in fact looking for applicants just like your son. With an 80+% rejection rate, there are no guarantees, but they are definitely worth applying to.
One additional note is that Wesleyan requires SAT subject area tests but they do not require the basic aptitude portion of the test.