A racial reckoning began years ago for the Guilford (Connecticut) school system, first with an episode in which a student wore blackface makeup to a home football game and then a fraught debate over the elimination of its mascot, the Indians. After the killing of George Floyd, district leaders announced they were doubling down on efforts to address social justice and racism in schools and teaching materials. But an organized pushback in the overwhelmingly white community began last year with a petition for the superintendent’s removal. This summer, conservative activists won the GOP’s endorsement for school board, knocking out three...