“Yet” indicates that you may have previously shown signs of being a bad teacher, and that you are not *now* a good teacher, *but* that the speaker’s opinion of you has turned positive.

No, it's not sarcasm. It just means that they feel that person will become a good teacher in the future.

It's usually impossible to identify sarcasm without contextual or auditory clues. By nature, sarcasm involves saying words that don't match your intended meaning. This is why people often include a /s or /sarc tag with online posts to avoid confusion. "You'll make a good teacher yet" could be a sarcastic way of saying someone isn't a good teacher. Or it could be a way of expressing confidence that someone will become a good teacher with more education and/or experience. But without clues from context, online tags or tone of voice, there's no way to gauge the exact intent of the speaker or writer.

i believe it is something like this, I think with what you have shone me and the high level of commitment to learning the skill of teaching , you will become a good teacher (at a later date). eventually, yet implies in the future you will 'become', attain , something you are striving for.

It just means that you have a little more to go in order to become a good teacher, it is not taken as a negative statement. It's more "encouraging" if anything, in my opinion. Good question!