Seems to me that the number has to be relative to the overall size of your
organization and the layout of your galleries and rooms. Because of our
physical plant, we figure that we can accomodate no more than 200 students
at any one time, and maybe 250 per day overall. Other museums can do many
times that, while others can only handle one group at a time. And total
numbers visiting per day always have to fit into the school-day window of
9-3 or so, which focuses the effect.

More important is the way that you think about school groups as visitors.
I've fought for years the mentality that school groups "get in the way" of
other visitors...as if school children are some how NOT visitors. ????? When
you approach school groups in a positive light, as opposed to a necessary
evil, then their visitation becomes part of the overall pattern of visitors.

There's no doubt that attending to busloads of children each day takes some
organization, but so does a busload of seniors or tour groups. AND, many
times I have found that the programs set up for school groups work pretty
darn good with adult groups.

Just some thoughts.