I think teen readers of Twain are attracted by the vernacular language that
still sounds fresh, and the subversive undertones (I'd be curious to know
from teachers out there which of those two things students find more
attractive). This could also have something to do with why kids who read
below grade level prefer Twain's language over Milton's.  My favorite short
pieces for introducing young readers to Twain, long before they are ready
for the irony of HF, are the Story of the Bad Boy, and its companion piece.
Those are especially effective if read on a Sunday afternoon, when they are
freshly home from Sunday School.

Kevin Mac Donnell
Austin TX