IRS Publication 526 deals with Charitable giving.
Here's a link to the table of contents page;
http://www.irs.gov/publications/p526/index.htmlUnder "Contributions you can deduct" check out "Out of pocket expenses while giving services".
It does not mention anything about taking classes needed during the course of doing volunteer work.
Here is the alternative which may provide some method for doing what you seek.
IRS Publication 970 deals with education expenses and what is deductible;
http://www.irs.gov/publications/p970/index.htmlYou may find a way to deduct the costs associated with the classes you intend to take in that publication.
I am in no way a Tax attorney and for this question, if you can't find the answer on the IRS website, I would strongly suggest you ask an attorney. You should also consider calling your local IRS office directly. While it is possible you may spend some time on the phone finding the person who can answer your question, they are after all, there to help and if you are entitled to the deduction, they will tell you.
Good luck and kudos on your efforts.