LAFAYETTE, La. — A pole-vaulting runway extends about 125 feet from the side of the Duplantis family’s Acadian-style home, under a gate and into the backyard, where it ends at a foam landing pit, floodlit by a light made for an oil rig.

It was, until recently, the training site for the family’s youngest son, Armand. On April 1, at the Texas Relays, he vaulted 19 feet 4 1/4 inches, a national high school record, a world junior record and the highest jump at any level of international competition so far in this outdoor season. A vault of that height at the Rio Olympics last summer would have won a bronze medal.

Armand Duplantis — known as Mondo — is the only high school vaulter to have cleared 19 feet, and he has already done it twice this year. He is considered a medal candidate at the world track and field championships in August in London. This is extraordinary, given that Duplantis is only 17, a junior at Lafayette High School who competes in an event where athletes tend to reach their prime in their late 20s.

“It is off the scale; nobody’s seen anything like this,” said Earl Bell, a prominent pole-vault coach from Arkansas who won bronze at the 1984 Olympics in Los Angeles and once held the world record. “He’s the Tiger Woods of pole vaulting.”