It's why teachers become teachers – to make a difference to children's lives.
A fifth grade teacher called Jermaine in Atlanta, America, shared on Twitter a heart-melting letter left in his classroom by one little boy whose life he has had a big impact on.
His Twitter post sharing the letter which was left on his desk by student Markus, has been retweeted tens of thousands of times since it went up on 24 April.
"So much love and support in my mentions. I appreciate y'all. My eyes are red and puffy from crying," wrote Jermaine on his Twitter account, @mainey_maine.
Here's the letter in full.
To Mr J,
Thank you for being a awesome teacher and for being amazing! This school year was so fun and I enjoyed it because of you. I wish more teachers was like you. I will never forget you. I look at you like my Dad. I never met my real Dad but it okay because you treat me like I'm your son. You make me so happy. Always feeding me when I am hungry and hug me when I am sad. I will never forget you Mr J. I love you and I will never forget about you!