**Core Concept:** The anal stage of development is a term related to human development, particularly in the context of the Psychoanalytic theory proposed by Sigmund Freud. This stage is part of his model of psychosexual development, which includes five stages in total.

**Why the Correct Answer is Right:** Wilhelm Reich, a follower of Freud, described the anal stage of development. This stage occurs between the ages of 3 and 6 years and focuses on the child's exploration and mastery of toileting skills. The child is initially driven by the pleasure derived from defecation (anal erotism) and later develops guilt and anxiety around toilet training.

**Why Each Wrong Option is Incorrect:**

A. Sigmund Freud: Although Freud is responsible for the overall psychosexual development theory, the anal stage itself was described by Wilhelm Reich.
B. Jean Piaget: Piaget focused on cognitive development, not psychosexual development as discussed by Freud and Reich.
C. Jean Baker Miller: Miller is a feminist psychologist known for her work on gender and development, but not anal stage development.
D. Carl Jung: Jung emphasized psychological aspects and archetypes, not psychosexual development or anal stage.

**Clinical Pearl / High-Yield Fact:** Understanding the anal stage is crucial for pediatricians, psychologists, and child development specialists to guide children through this developmental phase effectively. Recognizing the normal anxiety and guilt experienced by children during this stage can help parents and caregivers provide appropriate support and encouragement for toilet training.