That sounds familiar, my teacher has lent me a red Barenreiter Urtext book 'Mozart Variations for Piano' I am working on 'Ah, vous dirai-je Maman' K265 (300e)http://www.youtube.com/watch?v=yy_UdK9SAMo
The notes at the front of the book say:
Twelve Variations in C Major on the French Song -
The anonymous theme was known in Paris at least from 1761 and became one of the most popular subjects for variations from 1770. Mozart evidently heard it in Paris and wrote a set of variations on it with an eye to his teaching activities. However, his handwriting in the autograph fragments mentioned below precludes the possibility that the work originated in Paris in 1778, as was generally assumed by earlier scholars. Rather, it is most likely to have been written down in 1781 during Mozart's first year in Vienna....