My first question is: what obligation do parents have to pay the dues? Are they required to pay in order to have their children participate in the band program? It seems unlikely that a school would deny kids the right to participate because their families could not afford the dues. (If it the dues are a required payment, they would not be deductible as a charitable contribution because the right to participate would be received in return for the payment.)

More likely, your dues are “voluntary” contributions that support the band program as a whole.  If that is the case, they can be deducted as charitable contributions.  But since they are voluntary, and not legally required, you have no legal recourse if the parents don’t come up with the money? If they have filled out a binding pledge form, you may have a legal obligation that is enforceable. But it doesn’t sound as though it would be economical to go to court to enforce it even if you have created a legal commitment. A collection agency would have a basis for seeking collection, but they can often generate more bad publicity than good money.

If there is no legal requirement to pay, you will have to market your program like every other charity.  I would ask others on your board to help cajole the families who can afford it but just haven’t come up with the money. I see no reason not to ask the kids who have graduated, including alumni who contributed during their marching years. You should emphasize how the money helps all of the kids, particularly those whose parents can’t afford to contribute fully. You can also talk about how the program may have to be cut back if you don’t have the funds to support it fully. I would also consider seeking corporate support from local businesses that would like the recognition in return for a relatively small contribution. Your recognition could direct a lot of customers their way throughout the year.