At age six, Yaakov was sitting in shul one day when some men who were studying needed to know a certain verse in the Song of Devorah (Shoftim ch. 5) but they could not find a Sefer Shoftim or a Chumash containing that Haftorah.  The men were amazed when the young boy proceeded to recite the entire Song by heart!  He explained matter-of-factly that his class in cheder (elementary school) had already studied the entire Sefer Shoftim.