pastry/dessert classes in Philadelphia
Some community night school programs (like Main Line School Night) offer fairly basic cake decorating classes. I don't think they offer classes on more formal pastries. You might look at the calendar for Viking Cooking School in Bryn Mawr to see if they have classes that sounds appealing to you. Also Albertson's Cooking School might or might not have pastry classes.
If you're looking for more of a one-off/one day then sometimes local pastry chefs will host these events at various places in the area, though I think that these are more demonstration and less hands-on.