I have been teaching a class for young students for six years now, and
this is a small database of knowledge compared with Adrian, et. al.  My
small quantity of experience, however, has never stopped me from giving my
opinion on an issue.  So here it is...
 
I have tried the mock dig and found that about 1 or 2 in 20 are enthralled
with the idea.  These are generally the students that love puzzles of
logic and word games.  Many other students found the mock dig to be fun at
first, but their interest level was inversely proportional to the heat.
 
So I began a project of surface recording of architectural remains and
archaeological features without excavation.  I do not excavate because I
have one week of class time to do the fieldwork and I only get hired year
to year to teach the course.  I could not ethically do a respectable job
if we broke ground.  The students do many forms of data collection, such
as soil sampling with a probe, tree coring for dendrochronology,
topographic map making, and feature drawing and recording.  We work on the
same site year after year.
 
I have found that the latter option has very clear advantages:
 
1.  The students feel that they are contributing to a _real_ research
program.  We spend a few hours of class time explaining previous years
work with photos of students doing it and I tell them how the data they
gather relates to significant research questions.
 
2.  A real site is recorded and comparative data is collected.
 
3.  The students really understand the preservation ethic- we discuss why
we are not going to dig- that digging is expensive, that digging requires
commitment, that digging takes a long time, and that digging would not
answer my research questions at this industrial site.... They understand
it well enough to explain why they did not dig to their parents and
friends.
 
(A few of you may have heard me discuss the results of this work so far at
the SHAs in Texas, I gave a paper in the industrial landscapes session on
a twentieth century brick plant in Pennsylvania.)
 
This is why I favor student volunteers on real sites.  When I am
working on a field school as a crew chief, I try to teach all of my crew
how to work with volunteers constructively so that after two field
school students learn to dig at a certain skill level, I can split up
their team and pair each with a volunteer.  In addition,
I have found that young students (12-16) are as reliable (if not more
reliable) than most college students (18-20).
 
My two cents,
 
Tim Scarlett