I've had the best and worst of teachers.
Though curiously, the worst teacher I ever had may have also been the best. I was in middle school, utterly convinced of my own failure in mathematics, trying to understand the words coming out of Mrs. Beagle's squeaky mouth with its many wobbly chins. And I can say that she put the Fear of Math into me.
"The Fear of Math" is something many children experience. Yet, after switching schools for the last time, no longer under the auspices of Mrs. Beagle's beady stare, I sat down and taught myself Calculus. It wasn't easy, but after six months of nothing but math, I realized I was quite good at it after all.
As it turns out, being bad at something is often the first step to being sort of good at it. But most of all, what I learned from Mrs. Beagle lingers in my mind: it is possible overcome the context of your environment.