The Collaborative International Dictionary of English v.0.48:

Teachable \Teach"a*ble\, a.
   Capable of being taught; apt to learn; also, willing to
   receive instruction; docile.
   [1913 Webster]

         We ought to bring our minds free, unbiased, and
         teachable, to learn our religion from the Word of God.
                                                  --I. Watts.
   [1913 Webster]

WordNet (r) 3.0 (2006):

teachable
    adj 1: ready and willing to be taught; "docile pupils eager for
           instruction"; "teachable youngsters" [syn: docile,
           teachable]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "teachable":
   apt, bright, clever, docile, educable, facile, formable, homely,
   humble, humble-looking, humble-visaged, humblest, impressionable,
   inglorious, innocuous, instructable, intelligent, least, low,
   lowest, lowliest, lowly, malleable, mean, modest, moldable,
   motivated, plain, plastic, pliable, poor, quick, ready, receptive,
   ripe for instruction, schoolable, simple, small, susceptible,
   thirsty for knowledge, trainable, undistinguished, unimportant,
   unpretentious, willing