Momtofour, College Board did a major overhaul on the AP Bio exam two years ago. That is why there are fewer 5s - they made the test harder (though my kid thought the MC was really easy, much easier than the old tests).

College Board also changed the foreign language tests a few years back - eldest took French prior to the change and German after (said the tests were very different, as you now need to know about culture, geography, etc.).

So the recent changes in score distributions are likely due to changes in the tests (and kids perhaps not being familiar with the new formats, as there aren't that many practice materials available).