John F. Kennedy sat in chapel a sinner, but not for the kind of offense we would one day associate with him. This was long before he met Jacqueline Bouvier and made at least half of the population melt in seeming perpetuity. In the early 1930s, his crime was decidedly juvenile.

Aided by the sons of America’s most influential families, young Jack—then a student at Choate—had successfully snuck firecrackers onto his elite boarding school’s Wallingford, Connecticut campus, and headed straight for the bathroom. That morning, during the obligatory daily assembly, long-suffering headmaster George St. John held up the defenseless victim—a badly injured toilet seat—for all to see.

St. John railed against “the muckers,” as he labeled the culprits, which Jack took to heart, though not in the way the headmaster likely intended. Inspired, the future president named his band of first-class troublemakers “The Choate Muckers Club.”

“What makes the whole problem more difficult is Jack’s winning smile and charming personality,” wrote Earl Leinbach, the housemaster of his dormitory at Choate. Jack proved to be an immensely frustrating, totally irresistible high school student—a confusing combination for the school’s faculty and administration.

Choate had known a very different student in the eldest Kennedy son, Joe Jr., but it had nonetheless accepted Jack after he failed the school's entrance exam for Latin. Twice. Still, he’d scored 119 on his IQ test, placing him in the top percent of Choate students, and that wasn’t the only reason they were interested in him. The Kennedys had generously donated a projector. “The School is thrilled Mr. Kennedy’s wonderful moving picture machine is to give its first performance this Saturday night,” St. John wrote to Mrs. Kennedy on April 14, 1932.

Choate House, Jack Kennedy’s residence hall in the third form (9th grade); Class of 1935 Yearbook Photo Choate Rosemary Hall Archives

But Jack, for his part, was also consistent with his early scores. “He learned not what you wanted him to learn, but what he wanted to learn,” wrote Harold Tinker, an English teacher tasked with tutoring Jack on spelling and punctuation. That was his best subject sophomore year, in which he earned an 81 and developed a lifelong love of Robert Frost. (He would later invite Frost to read a poem at his 1961 inauguration.)

In other subjects, however, he barely pulled a “gentleman’s C,” the kind of grade the sons of America’s gilded families could count on, managing just a 73 in French and a 69 in Latin.

Languages weren’t the only thing that plagued Jack. He contracted scarlet fever a few months before his third birthday, and from then on, his health was almost always in peril. He had chicken pox and frequent ear infections. He lost weight and blacked out at school. His appendix was removed and he injured his knees. Rose, his mother, often communicated with Choate during his sophomore year, when he practically took up residence in the infirmary. He suffered from chronic colds, boils, pinkeye, the discovery of astigmatism and, of much concern to Rose, fallen arches.

In 1933, she called it an “inherited weakness.” He remained in good spirits, even when a mysterious illness landed him in a New Haven hospital, and then Palm Beach, where he spent months away from school. Doctors feared leukemia, though tests were inconclusive. He returned to school, but spent much of the summer of 1934 at the Mayo Clinic in Rochester, Minnesota.

He learned not what you wanted him to learn, but what he wanted to learn.

Throughout it all, he kept losing weight, and by 16, he could no longer play the contact sports—baseball, basketball, football—he loved. There were brief hospital stays, but doctors found his symptoms bewildering, and offered diagnoses as banal as growing pains and as serious as cancer. They ordered endless medical tests be run, poking and prodding the teenage Kennedy until he could take no more.

He wrote vividly—if scatalogically—of the ordeal to his friends. “[The doctors] shoved everything from rubber tubes to iron pipes up it,” he complained to LeMoyne Billings, a classmate at Choate. “When I crap I don’t even feel it because [my rectum] is so big.”

Medical issues, as well as his winsome personality, were a part of Jack’s constitution, and would prove to be lifelong traits. In Profiles in Courage, for which he won the 1957 Pulitzer prize, Jack wrote about a back surgery that nearly killed him, omitting far more serious conditions that might have affected his political career, including Addison’s disease, a deficiency of adrenal hormones he managed with corticosteroids.

While his older brother, Joe Jr., excelled at Choate—he dominated in the classroom and on the field—it was Jack who demonstrated an undeniable intellectual curiosity. “[He] was the best informed boy of his year,” the headmaster remembered, and possibly the only student at Choate who personally subscribed to the New York Times.

Jack no doubt saw his own father’s name on the page. At the time, Joe Kennedy was the chairman of Franklin Delano Roosevelt’s Securities and Exchange Commission, but he still managed to check up on his son. “I would be willing to bet that within two years you will be as proud of Jack as you are of Joe,” St. John wrote after a disappointing visit to campus.

John F. Kennedy, ’Dunker’ the dog, and Lem Billings at the Hague, during their Europe trip. Corbis Historical Getty Images

Joe Jr. had graduated in 1933, allowing Jack to be even more, well, Jack. He doubled down not on his studies, but on his tom foolery, persuading his classmates to completely fill a student’s room with pillows. Hundreds of them. The unlucky fellow opened his door and found himself facing a wall of plump rectangles.

Choate certainly had a soft spot for Jack, but they eventually turned pessimistic about his ability to improve academically. “I’m afraid it would almost be foolishly optimistic to expect anything but the most mediocre from Jack,” wrote one teacher to St. John, who decided to “give [Jack and his band of pranksters] thunder.”

At Choate’s suggestion, Jack visited Prescott Lecky, a psychologist at Columbia University, who determined sibling rivalry was partially to blame. Instead of competing with Joe Jr., who their father erroneously thought was destined for the Presidency, Jack simply, in Lecky’s estimation, “withdraws from the race, so to speak, in order to convince himself that he is not trying.”

Jack probably didn’t believe he was destined for any position but primary holder of Joe Jr.'s shadow, either: “May we room together at Sing Sing,” he wrote on graduation photos to friends.

His peers, however, saw a different path for young Jack. Despite graduating 65th in a class of 110, John F. Kennedy was voted “Most Likely to Succeed.”

Independent Picture Service Getty Images

Alexis Coe is an historian, author of , and co-host of Audible’s podcast Presidents Are People Too. She’s writing a biography on George Washington. You can follow her on twitter and Instagram.