Emily Stout's heart raced as she and her crewmates jumped out of their ambulance on I-95 in Darien, Conn., on a sunny Wednesday afternoon. Slumped against a concrete barrier was a stunned-looking man, his leg bloody, his crushed car a few feet away. Within minutes, Emily and the others—Wells Landers, Annie Maybell and Kate Kevorkian—placed the victim in a spine-stabilizing collar, bandaged his leg, lifted him onto a stretcher and sped off to nearby Stamford Hospital, where they wheeled him into the ER. "Feel better, sir!" Emily called out.

They may stress over grades and dates, but for Emily and 58 other teen volunteers in the Darien Emergency Medical Service—Post 53, car crashes and heart attacks are all in a day's work. The sole ambulance service for this suburb of 20,000, the "Posties" take 1,450 calls a year, in which they perform CPR, administer oxygen and even help deliver babies. (An adult EMT with more training is on hand for such advanced procedures as inserting IV lines.) "They're superb," says Timothy S. Hall, Stamford Hospital's chairman of surgery. "I've had cases where patients wouldn't have lived without them."

Founded as an Eagle Scout project in 1969, Post 53 requires teens to pass a screening, then do 140 hours of training and take an exam to become certified EMTs. On call 120 hours each month, the high schoolers carry radio transmitters to class (teachers understand)—and drop everything when called. Once, "I had to leave three minutes before Harry Potter ended," Stout, a senior, recalls. The dedication pays off. Two years ago, a Postie crew helped revive Jim Cloud, 75, by performing CPR after he had gone into cardiac arrest. Says wife Sheilah: "They saved his life. They're magnificent."

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