I believe Sondheim wrote four musicals for Oscar's course, but I am often bad about detail. They were All That Glitters, Mary Poppins, Climb High, and something else?
There's a difference between writing a reprise and writing music thematically. Just because you hear a line of music again doesn't mean it's a reprise. A reprise is when you hear a song in a show again and there's almost nothing different about it, if anything at all. When Sondheim says he's against them it's because he doesn't understand why a character would sing unless they had some cause to, or why they would ever sing the same thing again since they have clearly gone through a lot of growth since the first time they sang that song.
I think this is kind of unfair of him because it's a very general statement and he has used reprises. A Little Night Music reprises Send in the Clowns at the very end. It's justified, so I agree that in places where it is justified, go for it. But it's a little shady to repeat a song for the express purpose of letting the audience hear it again.
FoscasBohemianDream, your statement was a little funny because Oscar Hammerstein wrote the lyrics and book of Showboat, and Rodgers music for Pal Joey.
TheEnchantedHunter, thank you. Sondheim is less the maverick than people accuse him of being. Supremely romantic and brooding, right down to the every note of his music (what unromantic composer could write any of Sweeney Todd?). He just doesn't deal in kitsch, like so many others. There is the difference.
yr ronin,
joey