Dr. Gradus ad Parnassum is a piano piece written by Claude Debussy, and is a part of a larger suite of (mostly, piano) pieces called Children's Corner.
It is several pages long, but ends up being quite short as it must be played quickly.
Its name is a take off of Clementi's theory exercises, called Gradus ad Parnassum. The piece is almost a theory exercise itself, as it is loaded with arpeggios, odd timing and left-over-right playing.