2 deficits of my own come to mind. I didn't learn the alphabet until middle school or so; I covered up my ignorance by knowing pairs of letters and simply looking it up whenever I needed to sort something. (In middle school I realized how silly this was and studied diligently until I could finally remember the alphabet song. For years after that, whenever I needed to know something, I would mentally sing through the alphabet song until I had my answer.)

Until 2 years ago or so, I didn't know the 12 months of the calendar. I got around this by generating a bunch of month flashcards for Mnemosyne. (The cards should be obvious, but if anyone really doesn't know how that would work, I can post them.) I'm still a little shaky but I more or less know them now.

These 2 methods may not be generally applicable.