I couldn't agree more. I saw Up the Down Staircase several times during its theatrical release because I had read the book and was such a fan of it. After seeing the movie, I could never read the book and not picture those fantastic actors in those parts. The movie was pretty perfectly cast, I think.
The current DVD is a pretty dirty transfer and will need some work that Warners may not want to pay for, but I certainly would love to have this in pristine condition.