Is he interested in grad school after college? If that is a factor then he really has the opportunity to do both-- Williams for undergrad opens up the opportunity to attend grad school anywhere. Part of the reason I chose Williams was because I would never have another opportunity to live and study here while Brown will still be available when I graduate. How important is class size? I really appreciate our small classes and tutorials so they were another consideration when I was making the choice a year ago. Research is super accessible at Williams and the students within both envi and physics form tight-knit, collaborative communities. I agree with the other responses: both are fantastic colleges, it really comes down to size and location preferences.