A 6-year-old girl from rural Maharashtra is referred for evaluation of a systolic ejection murmur detected on routine school screening. She is asymptomatic, plays normally, and has no dyspnea or chest pain. Vital signs are normal. On auscultation, there is a grade 2/6 systolic ejection murmur at the left upper sternal border, with a normal S2. Chest X-ray is normal. What is the most appropriate next step in management?