In an ideal world the student would be switched on and proactive in their training but glider clubs can be difficult to 'crack' as in feeling a real part of the scene and a feeling of belonging. In my experience that makes a real difference in the level of keenness from the student and along with social activities at the club can help bind them to the sport
At my club the instructors are rostered on and the students mostly fly with who ever is on duty. They are free to fly with any instructor by arrangement and some choose to do this. Here in New Zealand we have a structured syllabus that leads through to being a qualified glider pilot which goes some way to keeping good continuity between the different instructors.
http://www.gliding.co.nz/training/syllabus
One of the bigger problems I have seen in the last 8 years since my return to the sport is 'old worn out' instructors staying in the game for the free flying with students and trial flights. They only flew when someone else was paying and showed little interest in progressing the students through the syllabus. Fortunately for all concerned this has largely disappeared in the last couple of years. I would also like to be very clear that some of our 'old timers' are/were excellent instructors and with their years of experience are of great value to the club
Colin
http://www.glidingauckland.co.nz