Jack was very popular and had many friends at Choate, a boarding school for adolescent boys in Connecticut. He played tennis, basketball, football, and golf and also enjoyed reading. His friend Lem Billings remembers how unusual it was that Jack had a daily subscription to the New York Times . Jack had a "clever, individualist mind," his Head Master once noted, though he was not the best student. He did not always work as hard as he could, except in history and English, which were his favorite subjects. "Now Jack," his father wrote in a letter one day, "I don’t want to give the impression that I am a nagger, for goodness knows I think that is the worse thing any parent can be, and I also feel that you know if I didn’t really feel you had the goods I would be most charitable in my attitude toward your failings. After long experience in sizing up people I definitely know you have the goods and you can go a long way…It is very difficult to make up fundamentals that you have neglected when you were very young, and that is why I am urging you to do the best you can. I am not expecting too much, and I will not be disappointed if you don’t turn out to be a real genius, but I think you can be a really worthwhile citizen with good judgment and understanding."
Jack graduated from Choate and entered Harvard in 1936, where Joe was already a student. Like his brother Joe, Jack played football. He was not as good an athlete as Joe but he had a lot of determination and perseverance. Unfortunately, one day while playing he ruptured a disk in his spine. Jack never really recovered from this accident and his back continued to bother him for the rest of his life.
The two eldest boys were attractive, agreeable, and intelligent young men and Mr. Kennedy had high hopes for them both. However, it was Joe who had announced to everyone when he was a young boy that he would be the first Catholic to become President. No one doubted him for a moment. Jack, on the other hand, seemed somewhat less ambitious. He was active in student groups and sports and he worked hard in his history and government classes, though his grades remained only average. Late in 1937, Mr. Kennedy was appointed United States Ambassador to England and moved there with his whole family, with the exception of Joe and Jack who were at Harvard. Because of his father’s job, Jack became very interested in European politics and world affairs. After a summer visit to England and other countries in Europe, Jack returned to Harvard more eager to learn about history and government and to keep up with current events.
Joe and Jack frequently received letters from their father in England, who informed them of the latest news regarding the conflicts and tensions that everyone feared would soon blow up into a full-scale war. Adolph Hitler ruled Germany and Benito Mussolini ruled Italy. They both had strong armies and wanted to take land from other countries. On September 1, 1939 Germany invaded Poland and World War II began.
By this time, Jack was a senior at Harvard and decided to write his thesis on why Great Britain was unprepared for war with Germany. It was later published as a book called Why England Slept. In June 1940, Jack graduated from Harvard. His father sent him a cablegram from London: "TWO THINGS I ALWAYS KNEW ABOUT YOU ONE THAT YOU ARE SMART TWO THAT YOU ARE A SWELL GUY LOVE DAD."