Most children stop using daytime diapers between the ages of two and four, although nighttime training can be more difficult and may not be completed until around five or six years of age. For Alejandra Pérez, supervisor of pediatrics and neonatology at Sant Pau Campus Salut Barcelona, it is key to understand that sphincter control is not a habit learned through repetition, "but rather a maturational milestone acquired when the child's body is physiologically, cognitively, and emotionally ready." Neurologically, Pérez continues, "it involves a transition from an involuntary reflex action (where the bladder empties automatically) to a voluntary and conscious act under cortical control." Forcing this process prematurely, therefore, "is ineffective and can generate frustration, anxiety, and unnecessary conflicts, as each child has their own pace of nervous system maturation."