Is teached a word?

No, “teached” isn’t a word in standard English. The past tense of the verb teach is taught. Teach is an irregular verb, and taught is both the simple past tense form and past participle.

You might occasionally encounter “teached” used humorously or as part of a dialect. But it is incorrect in formal writing.

You can use the QuillBot Grammar Checker to find the correct past tense of teach.