He's talking about Law School of course - that's where promising students are drafted into the Supreme Court clerk position that's the first step on the cursus honorum to becoming a Supreme Court Justice. Undergrad doesn't matter as much except inasmuch it gets you into the prestigious law schools.
Um, Sandra Day O'Connor went to Stanford for undergrad and law school.
Also, this is a thread that's largely about undergrad, so I'm not sure Rayiner was talking about law school.
There are different rankings for law schools, and Yale has been considered the most prestigious for many years. I think SLS nabbed the top spot various times in the last decade, but Harvard is definitely not the uncontested leader in law schools.