The Collaborative International Dictionary of English v.0.48:

Untaught \Untaught\
   See taught.

WordNet (r) 3.0 (2006):

untaught
    adj 1: lacking in schooling; "untaught people whose verbal
           skills are grossly deficient"; "an untutored genius";
           "uneducated children" [syn: unschooled, untaught,
           untutored]

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "untaught":
   Gothic, Philistine, amateurish, barbarous, benighted, bookless,
   deceived, empty-headed, functionally illiterate, grammarless,
   heathen, hoodwinked, ill-educated, illiterate, know-nothing,
   led astray, lowbrow, misinformed, misinstructed, mistaught,
   nonintellectual, pagan, rude, semiskilled, unaccomplished,
   unbooked, unbookish, unbooklearned, unbriefed, unbusinesslike,
   uncoached, uncultivated, uncultured, unedified, uneducated,
   unendowed, unerudite, unfinished, ungifted, unguided, uninitiated,
   uninstructed, unintellectual, unlearned, unlettered, unliterary,
   unpolished, unprepared, unprimed, unprofessional, unread,
   unrefined, unscholarly, unschooled, unskilled, unstudious,
   untalented, untrained, untutored