A child prescribed methylphenidate presents to the pediatrician's office for a follow-up appointment. Which clinical finding indicates the dose is therapeutic?

A. The caregiver reports the child is fatigued: Fatigue is not an expected therapeutic effect of methylphenidate and may indicate overmedication, sleep disruption, or other adverse effects. Monitoring energy levels helps assess tolerability but does not confirm therapeutic benefit. B. The child's apical heart rate is elevated: Tachycardia is a known side effect of stimulants like methylphenidate, but it reflects a potential adverse cardiovascular response rather than therapeutic efficacy. Heart rate monitoring is important for safety. C. The child reports they do not feel hungry: Appetite suppression is a common side effect of methylphenidate and can lead to weight loss or nutritional concerns. While expected, it does not indicate that the medication is achieving its intended behavioral effect. D. The child has an improved ability to focus: Enhanced attention, concentration, and task completion demonstrate the desired therapeutic effect of methylphenidate in managing attention-deficit/hyperactivity disorder. Observing improved focus confirms the dose is effective for symptom control.