When I was in school, teachers didn't know about dyslexia, ADHD, or PTSD. They didn't understand my stutter, so I stopped talking, and just did the best I could to keep up and not get noticed by my teachers anymore.
They did notice. All through my youth I was told I was "stupid," "deliberately acting dumb," and "failing tests on purpose." I was told I would never graduate. I got lumped in with the bad crowd, and wore my "dumbness" with pride. Until I met my 8th grade math teacher.
Math was always my worst subject. Dyslexia turns timed multiplication tests into an instant panic attack. My former math teachers told me that they let me pass their classes just so they wouldn't have to deal with me again.
But this one teacher. He kept me after class and helped me with homework. He walked me through tests so I would slow down enough to finish them. And then one day, out of the blue, he told me I was smart, and that my brain just worked too fast for anyone else to keep up.
In all of my 15 years, nobody had ever called me smart.
With that one little comment, I started passing classes. I ended up graduating not only high school, but college, too. My stutter slowed, and now, years later, I still truly believe that I'm smart.
That one math teacher that took time out of his overworked days to tell the dumb kid she was smart. That's what stuck with me.