I have given ad-hoc tution on Java programming at this fast food restaurant A&W at PJ which unfortunately has now closed down.
It's memorable to me because I had 2 students who failed their term exam and were retaking the subject. Students are weak in the subject which is not uncommon and not surprising because it was something very foreign to them. I was surprised when I saw how fast they understood and absorbed the material I gave them. Surprised because from experience, I know such students do not fail subjects. These were A plus calibre students! So the only conclusion was their teacher was really bad. Skipped over teaching some key topics essential for the exam or just presented them poorly.
This experience resonated deeply with the 1984 Karate Kid's powerful quote: "There is no such thing as a bad student, only a bad teacher." I am very average and definitely do not claim to an exceptional teacher or anything but it goes to show a bad teacher can lead students astray.''
Oh, both these students scored A's during their retake exams, something I had not a single doubt would be the result (which is saying a lot since I can't say that for my other students)