@HRSMom, distressingly, for the Supreme Court, that is true.
Note that this is a fairly recent phenomenon.
Look at the giants of the Warren Court:
Warren attended Cal for undergrad and law school.
Hugo Black got his JD from 'Bama.
Felix Frankfurter did go to HLS but went to CCNY for undergrad.
William Douglas went to Columbia Law but attended Whitman for undergrad and picked cherries with migrant workers there.
Robert Jackon attended Albany Law School.
William Brennan was UPenn and HLS.
Potter Stewart was Yale and YLS.
Abe Fortas was YLS but went to undergrad at Rhodes.
Thurgood Marshall was Lincoln University and Howard Law.
John Harlan went to Princeton undergrad but New York Law School.
Contrast with the current Supreme Court:
Every single current justice attended YLS or HLS. Every single one except Clarence Thomas attended an Ivy or equivalent for undergrad. Heck, HYPS, making up a small percentage of even the Ivies/equivalents tier, contributes 2/3rds of the current Supreme Court.