Sylvia Plath wrote this essay for her Smith College course "Deutsche 12," and the typescript carbon, in German, titled "Wie Ich Einmal Kleinen Bruder Neckte" is in the Lilly Library's Plath mss. II, Box 8, folder 19, "Prose-fiction." I would call it nonfiction. Because I have never seen a translation or even a discussion of this essay, here it is in English:
How I Once Teased Little Brother
It was in 1938. Autumn had come and the sky was blue and clear, the sun glowed like a diamond, and the little leaves were very colorful. Afternoons I hopped joyfully on my way home. I thought the whole world was a wonder, in my first year of elementary school.
My little brother, who was too young to attend elementary school, was very jealous. Every day I bragged that I could read and write, and my father and my mother were very proud of me.
My little brother stayed silent. Finally he said, in a clear, loud voice: “I don’t go to school; I do something better! I live every night on the other side of the moon. . .”
My father and my mother now listened to the inventive story my little brother told. Now I was the silent and jealous one. He was too smart for me.
Plath enrolled in this intermediate-level German course in her senior year, spring 1955, then dropped it to better prepare for her comprehensive exams (letter to Aurelia Plath, 25 April 1955). Aurelia Plath mentions in her preface to Letters Home young Warren ("little brother") Plath's "Other Side of the Moon" adventure tales, spun when he was two and a half years old.