Setting our students up for dissapointment?

For the past few months I have had the pleasure of singing in Master singers for several friends' recitals. While the rehearsals are full of growth and great technique on both the conductor's and the singers parts, I find that the preparation time for this major event in a student's life is far too short. When the class can not provide a large enough or balanced enough ensemble for the conductor, and the conductor must find others who may not be able to make it to these rehearsals, it puts that person in a very difficult spot. When one only has two or three weeks before a performance, missing one rehearsal is missing a lot and some volunteers for these recitals can only make a couple of rehearsals of the five day rehearsal week! I think to hold a conducting student to such high standards under these conditions is to set them up for dissapointment, mostly because they are working so hard to prove themselves. Is this fair to do to our students? How often do we do this in our own classrooms? Telling our students to reach for the stars, but only providing them with a decrepit step ladder?