One other somewhat valid reason for looking down on a Pro/Am couple, especially when it's a pro gentleman, and a female student might be that the female student has the benefit of a professional for the lead. She might be able to get away with a little more since she's got a pro to lead her around the floor. I'm not saying women who dance pro/am aren't good, it's just I think that the dynamic is easier than a male student and a female instructor, or two amateurs. I've seen plenty of women who have only done pro/am, and looked amazing at it, but take away the pro, and they look a little lost.