A good teacher makes a difference in children's lives.
How can teachers be sure that they've made a difference? The children remember them. Not just for a little while, but forever. Even when you're an adult, you still remember the one or two really good ones.
I heard a story about a special teacher yesterday, via someone who must have been taught by them around 15-20 years ago. Despite being moderately famous now (actor, something of a YouTube star etc.) this person still remembers their teacher. They even shared the story that they loved coming to school so much that they were frustrated and disappointed when they had their tonsils out, and couldn't come in every day to spend time with their favourite teacher.
See - I always knew this teacher was brilliant, and a particularly wonderful person.
But I would say that.
I married her.