* Learn: This is probably the closest antonym if you're considering the transfer of knowledge. Teaching implies imparting knowledge, while learning implies acquiring it.
* Unteach: This refers to the process of removing or correcting previously learned information.
* Ignore: If you're thinking of the act of guiding or instructing, ignoring is the opposite of actively trying to impart knowledge.
* Misinform/Disinform: These are opposites if you consider the *accuracy* of what is being conveyed. Teaching implies accurate knowledge, whereas misinforming or disinforming is giving incorrect information.
The best opposite will depend on the context.