WASHINGTON, July 31—Sen. Lamar Alexander (R-Tenn.), the senior Republican on the U.S. Senate education committee, on Tuesday joined committee members Sen. Rand Paul (R-Ky.) and Tim Scott (R-S.C.) along with Senate Republican Leader Mitch McConnell (R-Ky.) and Sen. Mike Lee (R-Utah), in hosting a forum on school choice, where the...