Very generally speaking I have noticed that many men I paddle with feel successful in a rapid/river if they make it to the bottom alive where women seem to expect themselves to get through the rapid(s) exactly as they had planned to, without so much as a bobble, and without wasting a stroke.  Men and women can both be perfectionists, but it seems in paddling that more women expect perfection of themselves.  In my own personal experience this is because if I don't do something well (read "perfect") then I begin to think of all the horrible things that could happen if I screw up in a more dangerous rapid! 

BTW... I think it is great that you are teaching an all womens' class!!!  I love teaching all women groups.  I think women feel more free to learn in their own way when they aren't surrounded by guys who tend to be more willing to just go for it (probably because they are thinking things like, "oh... I must really suck at this because everyone else is doing things I am not" and "I guess I"m just too scared to do this since everyone else is willing and I 'm not"  etc...  Plus... I have been in classes where beginner men start giving "tips" to beginner women... not a good thing ;)