Come to think of it, Ebbie, I guess sourdough recipes are all sponge recipes. (I've never tried my hand at sourdough breads.)

A sponge recipe simply means that some of the flour is stirred into the yeast mixture, and allowed to rise for several hours before the rest of the flour is stirred/worked in. It can be a bit of a time saver, since you can prepare the sponge and let it rise overnight, and a bit less laborious to ultimately get all of the flour worked in. that additional 1/2 rise may make the dough more forgiving of insufficient kneading. Can't remember if the recipe called for adding additional gluten. Just remember it resulted in a much lighter loaf than most completely whole wheat recipes.