Teached

"Teached" is a nonstandard and grammatically incorrect past tense and past participle form of the verb "teach." The correct past tense and past participle form is "taught." The use of "teached" is generally considered an error in both spoken and written English. Its occurrence is rare and primarily found in informal contexts or as a result of a speaker or writer applying regular verb conjugation rules to an irregular verb. The irregular verb "teach" follows the pattern of "teach, taught, taught" for its principal parts.

Therefore, "teached" should be avoided in formal communication and replaced with "taught."