The best thing ever to happen to me, bar none, would be my grade 4 teacher, being the third school I went to that year from moving so often. I went from a not particularly bright kid, to being on the grade 8 math team, and after her i hadn't learned nearly anything in school until grade 10 or so. She was that good. I tried tracking her down a few years ago but she died when I was in grade 7 or so (I'd moved about 7 times since she was my teacher, my family likes to move) so I wrote her family a card telling them how much their mother meant to me.