“Upper class,” as used in this book, means that at least one parent—and usually both—graduated from college. The author also occasionally uses the terms “college-educated” or “rich” in describing these families.

“Lower class,” as used in this book, means that neither parent went beyond a high school education. These families are also sometimes described as “high school-educated” or “poor.”

“Middle class,” as used in this book, generally means that the parents had some college education but may not have graduated.