the child , who has not been named , suffered fatal injuries after jumping from a second-story window in dumont , new jersey last month .
a report into the incident has revealed he became angry after a classmate failed to say ` checkmate ' after beating him in a match at recess .
he then cried in a corner and wrote a note to his opponent , but told him to wait to open it ; the contents of the note have not been shared .
an aide then saw the boy climbing on shelves and out a window .
the boy 's classmate revealed that he had said on several occasions that he was going to jump from the window - but he thought he was joking .