Art Appreciation without Wagner?

I'm in High School (a Junior), and it's a requirement to take Visual Preforming Arts (or Art Appreciation) in order to graduate. Basically it teaches you about Art, Music, Dance, (etc.) of other cultures. Right now we've just left Clicalism (before that Baroque) and we're going into the modern era. So I'm huge on music right, and we've been learning about Handel, Palestrina, Mozart, Bach, Beethoven (the works), and we just went over opera. They left out Wagner. His operas do represent rather new ideas in music. He basically developed the leitmotiv with his style of writing his own libretti. His works influenced those of many composers such as Debussy (who we ARE studying as of present), and Schoenberg (whom I doubt we'll cover). So tell me, what would be your best reason for leaving out a rather important composer.