Neither schools "have grades." Both, however, provide enough performance indicators (ie: Hs) for employers to get a sense for who falls within what quarter of the class.
Actually, having science degrees can be very important for Environmental Law (and it's becoming more and more so). The OP should think about a joint degree regardless of where he (she?) ends up. Stanford has the IPER program (http://e-iper.stanford.edu/home
) which provides a joint JD-MS in the Environment and Resources in no extra time at no extra cost. I don't know much about Yale's offerings in this department--how many law classes do you have to sacrifice to get a joint degree? Can you get it in 3 years? Do you have to pay more?
Additionally, at Stanford you have the option of continuing on with clinics for ~3 credits after doing a clinical quarter. Ask any lawyer if you'll get more experience working on cases full time, or doing it as a 3rd or 4th case. I don't think there's a whole lot of question that, if you want, you can get more clinical experience at Stanford than about just about anywhere else (full time clinical quarter + continuing on as an "advanced clinic" student along side of your other classes).
To some extent, the above is all beside the point. There are little factors here and there that might make one school seem to stand out more than the other (Stanford's better for the 9th Circuit, Yale's better for the 2nd...etc), but none of these are nearly as important as your performance at either school, which is going to be pretty heavily influenced by your happiness. The sense I get is that most students at both schools are pretty happy (at least that's the case at Stanford), but there's also a ton of self-selection going on between the schools--I don't know that necessarily everyone at Stanford would be happy at Yale, or vice versa. It's SO easy to get caught up in the "nitty gritty" of things, especially on this board--the fact is that a 3% advantage in clerkship placement here, or a 4 point environmental ranking advantage there (yes, I just made up those numbers) is just not going to impact your experience, performance, or job prospects in any noticeable way. Your happiness, however, will.