We have only used group volunteers on occasion. We don't have any outdoor needs and really cannot use volunteers for major indoor tasks like painting or cleaning. We tried engaging college fraternity/sorority service groups to help out on weekends when we had special events and big attendance. The idea was that they would help people find their way to various activities. But without the possibility to do training in advance they were not good at way-finding and tended to hang out together. The problem was our inability to give them the training needed. This is also an issue in engaging corporate volunteers since having them come in advance for training is a challenge.
For many groups, they have a specific date in mind when they want to volunteer, and that usually doesn't match needs.
I have been turning down group requests but save the contact information just in case staff come up with something. Every now and then I will send out an all-staff e-mail to see if anyone has a project, but staff understand that they would need to invest a good amount of time in training (even for the simplest tasks) and for supervision.
Stretched as all of us are for time, engaging a group just doesn't help - even if the potential for later corporate funding support is there.
Lois Kuter
Academy of Natural Sciences of Philadelphia