In second grade, I teach the major styles of art: Realism, Abstract and Impressionism.
One of my proudest teacher moments came years ago, when I walked past a classroom and heard the teacher starting to teach abstract words. I noticed the word abstract written on the board, so I hung around to hear more. Several students related what they had learned about abstract art in my class.
This is my favorite way to teach Impressionism.
To finish, I let students use paper edgers (we call them "crazy cuts") to trim a paper frame and decorate with scrap paper. The results are not perfect, but charmingly child-like. They make a wonderfully colorful display.