It seems rude to evaluate volunteers. Do we really have to?

Summary:

When people are working because they believe in the importance of the task, it is especially important to let them know when they succeed and when they fail.

Experienced leaders and directors of volunteer programs have observed over
and over again that lack of feedback and direction can drain the energy from
a volunteer program. Directly stating goals and holding people to
reasonable standards in achieving them is essential to the continuing
success of volunteer projects. The way the evaluation process is conducted
may well be different when the subject is volunteer performance, but the
need for doing it is no less strong.

See "Volunteer Evaluation" by Steve McCurley and Rick Lynch accessible via
CASA Nuts and Bolts Volunteer Supervision section at
http://www.casanet.org/program-management/volunteer-manage/voleval.htm.

CASANet has a great
deal of volunteer-related material; check http://www.casanet.org/.