This incident reflects the personal history of Sylvia Plath's mother, Aurelia. Brought up to speak German by her two Austrian-born parents, Aurelia Plath could not speak English when she started school, and she did indeed experience some persecution from the other children.
Her experience of prejudice and hostility was shared by many immigrants of German extraction in America during the First World War: the Red Cross barred individuals with German surnames from joining their organisation; in Minnesota, a minister of the church was tarred and feathered for praying in German with a dying woman; in Cincinnati, the public library was asked to remove all books written in German from its shelves; and in Iowa, the governor banned the speaking of any foreign language in public places or in schools.
On the whole, the German American community (including Sylvia Plath's grandparents) responded by making greater efforts to integrate into the English-speaking community. Many Germans also chose to americanise their surnames, changing, for example, Schwarz to Black; Müller to Miller; Zimmerman to Carpenter, and so on.