(CNN)For 12-year-old Rylee Anderson, the algebra concept of graphing a function just didn't make sense.
Since her classes are now all remote due to the coronavirus pandemic, Anderson emailed her teacher for help, rather than ask for it in the classroom.
She expected some emails, or maybe even a phone call from her teacher, Mr. Chris Waba.
But then the doorbell rang -- and she saw Waba, standing on her porch, holding a whiteboard and marker, ready to teach.
Anderson, like most students in the US, has been out of school and learning virtually because of the coronavirus outbreak.
The Madison, South Dakota student said while trying to complete her math homework, she couldn't ask her parents for help because they weren't home. Plus, she said, they wouldn't have been much help anyway.
"My mom got all the questions wrong when she helped me before," Anderson told CNN.
When Waba received Anderson's email, he responded -- but could tell she was still struggling with the lesson.
Knowing that she lived just right across the street, Waba picked up his whiteboard and headed over for a special one-on-one lesson, one that still complied with social distancing rules.
For 10 minutes or so, Waba squatted on Rylee's porch as he went through three math equations. Rylee stood on the other side of the screen door, nodding her head as she followed along and took notes.
"He made it easier to understand," Rylee said. "I appreciated him coming over."
Rylee's dad, Josh Anderson, who is the head coach of Dakota State University's football team, shared the moment on Twitter. His post has since garnered hundreds of retweets and thousands of likes.
"The picture just shows the length that which teachers will go to help their students at any cost during these times," Josh Anderson said.
Waba, who has been teaching at Madison Middle School for 27 years, said it was a spur-of-the-moment decision.
"I'm a better communicator face-to-face than (on) the telephone and I think students learn better that way," Waba said. "Teachers all across the nation have been thrown into a situation like this. I think we're all more comfortable being in front of our classes and that's where we'd rather be."
By the end of their lesson, Waba said he could tell Rylee finally understood the concept because she smiled and thanked him.
"That's what teachers are looking for, those smiles," Waba said. "That's the joy of being a teacher and that's what we do it for."