Interesting thread..
The system we use at my club is almost the ideal system described by
Stefan. We split the students into groups of 3-5 per instructor and
they always fly the same day, usually every Saturday or Sunday morning
and sometimes there is a weekday group. They start together and stick
with the same instructor for the entire course, normally making two
flights per day. When they are about to solo or having difficulties we
often have them fly with another instructor to make sure we didn´t
miss something or for the student to get a different perspective.
Along with the normal ground instruction by the instructor, we have 5
or 6 Saturday evening classes for all of the students with
presentations by specialists on Aerodynamics, Flight Maneuvers, Ground
Operations, Meteorology, Safety, Airspace, Regulations, etc.
One of the instructors is a psychologist and he interviews all of the
applicants before they begin. This works very well for profiling the
students and finding the best match with the instructors and also as a
way to filter out the undesireable ones.
Intstructors don´t get paid but we get a free tow for every eight
instruction flights..

We are near a very large city so there is no shortage of applicants
and we don´t have enough instructors to take all of them. Usually we
turn out around 15-20 pilots per year but only a fraction of them are
still flying a year or two later. Getting them to stay is what we see
as the biggest problem. My opinion is that for many people the sport
just takes too much commitment.
It would be great if it was cheaper and simpler but then I guess it
wouldn´t be soaring..

Regards,

Juan Carlos