When he first started at Hendersonville High School in Tennessee, 15-year-old Sergio Peralta tried to keep a secret: He’d been born with a right hand that hadn’t fully formed. Over the years, he’d gotten used to doing almost everything with his left hand, but as the new kid at school, he didn’t want everyone to know. Eventually though, an engineering teacher found out—and soon three of his students offered to build a robotic hand for Sergio. Using online models and a 3-D printer, the students spent four weeks designing, sizing, and 3-D printing a prosthesis. Then they put their invention to the test with a game of catch, and for the first time, Sergio was able to grab a baseball with his right hand. The students say the experience made them consider how engineering can be applied in practical and meaningful ways. As for Sergio, he was touched that his classmates wanted to help him. “No one has ever offered me this stuff,” he told CBS News. “They changed my life.”