This randomized controlled clinical study compared supine mini percutaneous nephrolithotomy versus flexible ureteroscopy for the management of dense lower calyceal renal stones measuring 1-2 centimeters (≤20 millimeters) with stone density greater than 1000 Hounsfield units in school-age pediatric patients aged 6-12 years. Participants were randomized to undergo either supine mini percutaneous nephrolithotomy with laser lithotripsy or flexible ureteroscopy with laser lithotripsy. The study assessed stone-free rate on non-contrast computed tomography of the urinary tract at 1 month postoperatively, along with operative time, fluoroscopy time, intraoperative and postoperative complications, and length of hospital stay. The trial has ended.