Kindness from a teacher, simple kindness, can be just as Fran said. Something that will never be forgotten.
I think from SK through grade 8, all of teachers at my school(s) knew pretty well what was going on in my home with my mentally ill mother, abuse, lack of food, and the eventual cycle through foster homes. No teacher ever came to discuss this stuff with me, they knew I had social workers and counsellors and on and on. And probably they didn't know what if anything they could have done to help anyhow. Although i think all my elementary teachers were really wonderful (I lucked out growing up regarding great schools), a couple stand out. In hindsight I can see they were showing me kindness as their attempt to impact my life. They probably will never know how much they did. I remember a teacher rigged a school raffle so that I'd win (he winked at me when I caught him picking through the slips with names for mine) and he knew it would make a world of difference for me to win the prize (It was free pizza on weekly pizza days, for the entire school year complete with the milk cartons you could buy on pizza day ... and maybe once a week I'd actually have a lunch to bring with me to school, that prize made me relish going to school on Wednesdays and sometimes was the only food I had that day). Another teacher noticed my love for reading, all i was allowed at home for personal property for about a 2 year period was books. To this day I'm a avid reader and my only "neat" skill is that I can speed read which is handy! Anyhow this teacher slipped me a few books throughout the year that he thought I'd enjoy, I read them until they were falling apart. On the final day of school before the summer, he asked me to wait a minute at dismissal. He had an entire set of books for me, all the traditional classics. Brand new in a neat wooden collectors box/bookcase. He told me he'd finished them so was just passing them along to me. But they were new, no bindings broken, never been opened. I didn't realize until I was older how he had gone and spent all that money to ensure I'd have something to keep me busy all summer and to go to the land of fiction as an escape from my home life. That was a summer that I went from being a big reader, to a book worshiper.
Yet again, another teacher simply always went out of their way when I did something good (a good grade, etc) to ensure I was told she was proud of me and how I applied myself and worked hard and that she believed i'd really be able to accomplish anything I wanted in life with that attitude etc. I would glow with the praise, simple as it was. She knew I wasn't getting it anywhere else, and she made sure I experienced a female role model expressing pride in me and helping me believe in myself.
Working with kids might even feel thankless at times. I hope that you have a sense of how valuable your role is and the difference you certainly do make.
(((Hugs))) Thank you for doing what a lot of us couldn't do every day. Chin up and i hope tomorrow is a better day for you.