The Collaborative International Dictionary of English v.0.48:

Mistaught \Mis*taught"\ (m[i^]s*t[add]t"), a. [See Misteach.]
   Wrongly taught; as, a mistaught youth. --L'Estrange.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Misteach \Mis*teach"\, v. t. [imp. & p. p. Mistaught; p. pr. &
   vb. n. Misteaching.] [AS. mist[=ae]can.]
   To teach wrongly; to instruct erroneously.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "mistaught":
   Gothic, Philistine, barbarous, bookless, deceived,
   functionally illiterate, grammarless, heathen, hoodwinked,
   ill-educated, illiterate, led astray, lowbrow, misadvised,
   misdirected, misguided, misinformed, misinstructed, misled,
   nonintellectual, pagan, rude, unbooked, unbookish, unbooklearned,
   unbriefed, uncultivated, uncultured, unedified, uneducated,
   unerudite, unguided, uninstructed, unintellectual, unlearned,
   unlettered, unliterary, unread, unrefined, unscholarly, unschooled,
   unstudious, untaught, untutored