Scritch Scratch We Have Nits by Miriam Moss

One day a tiny insect, no bigger than a freckle,

            climbs into

Miss Calypsos's classroom. Nobody notices until . . . 
  . . . Polly scritches.
           Joshua scratches 
                 and soon the whole class is scritching and scratching.

An irresistibly catchy text and zany artwork -- head lice have never been so much fun.