John F. Kennedy attended the Riverdale Country School, a private school located in New York City from the 5th through 7th grades. Here is one of his report cards from 1930. Note that JFK far from a straight A student at this age.  

A postcard from JFK to his mother on a class trip to the U.S. Capitol in Washington D.C. 

JFK attended Choate, a prestigious boarding school in Wallingford, CT from 9th through 12th grades. Here is one report of his behavior, focusing on the "lack of neatness." John and his friends that Choate were known to be rebellious. When they exploded a toilet seat in the school with a firecracker, the headmaster called the culprits "muckers." John then named his group of friends "The Muckers Club." Even though John finished only 64th in his class of 112 students, he was voted "most likely to succeed" in the Choate yearbook.