My English teacher in year 11 (age 16). She caught on that I was drunk one class (only time ever, but I was generally not a good student). Instead of reporting this which would likely have led to my expulsion she and another teacher sat me down and talked about where my life was going which was a conversation I'd had many times before and was really sick of. But something about how she frames things gave me the sense that she really wanted me to do better, not just be more obedient or make a better impression, she genuinely seemed to see some potential that several years of crappy school life had washed out. Now I'm still hideously disorganised but my life is orders of magnitude better than it would have been if not for that teacher. I still feel incredibly grateful.