Yale 1L here, contributing VERY anecdotal evidence:
- Roughly half of the 1L class seems to be from Ivy League undergrad schools. I'm basing this on an exercise we did during Orientation where we divided ourselves in groups on different dimensions, and one of the questions was whether or not we had attended an Ivy for undergrad. The group I was in for this exercise had about 50-60 students, and as I said, roughly half had gone to Ivys for undergrad (and of course, there are also quite a few people who went to Stanford, Berkeley, and other non-Ivy but still prestigious schools).
- If that sounds discouraging to some of you, don't be too discouraged, because I definitely did NOT go to a particularly prestigious school for undergrad, and I know plenty of others who are in the same boat. I also didn't get a PhD or a Fulbright or a Rhodes (although again, plenty of my classmates have done one or more of those things).
- There are LOTS of 1Ls who went to Yale for undergrad (they definitely seem overrepresented). Of course, that could be because lots of Yale undergrads apply to Yale for law school, because they had a good experience during undergrad or for whatever other reason. But I suspect that there's at least a little bit of preference given there, especially since professors are involved in the admissions process.
Again, unlike some of the (much more reliable) evidence posted above, the reason for these things could just be that more Yale/Ivy league undergrads applied, or that their LSATs were higher (which is very likely), or a number of other things. Still, it surprised me and seemed disproportionate based on what I was expecting to see.