What I've always learned is American Classicism is political writings, such as the Delcaration of Independence, the Federation Papers, and some stuff by John Locke. There's other stuff obviously, but it's just the first things that came to mind. Don't rely too much on this, but that's just what I've been taught. Your teacher could consider it something else completely.
http://staff.gps.edu/gaither/literary_movements.htm
http://www.enotes.com/american-history-literature-cc/classical-literature
http://www.answers.com/topic/classicism