(CNN)Damien, 13, didn't believe it when he found out his new foster parent would be his math teacher, Finn Lanning.
A teen needed a stable home to make the kidney transplant list. So his teacher took him in
"The previous two foster homes said that they were stable," the seventh-grader told CNN with a hint of disappointment in his voice. "I didn't think that this one would last either."
Lanning and Damien first met at the beginning of the school year in August 2018 at the AXL Academy in Aurora, Colorado.
The teacher said he knew right away that the boy was special. "He is well-mannered, polite and exceptionally smart," said Lanning, who asked that Damien's last name not be used.
The teenager also faces a lot of challenges.
When he was 8, Damien's kidneys failed, and he went on dialysis.
He has moved through many foster homes over the years. This instability had kept him off the list to receive a kidney donation; his itinerant life raised the risk of transplant failure.
"Since his diagnosis, he has had to live in the hospital. One stay was a year. Others were a couple of months. That was the result (of) a lack of suitable placement," Lanning told CNN.
Any guardian must be trained to meet Damien's needs. The boy spends more than 12 hours each day connected to a home dialysis machine and has a restrictive diet.
"No way!" Lanning recalls thinking of the demands that would face him. " 'This is not something that I'm going to do.' But as time went on, I felt a call to engage with it. I couldn't just not do it. I didn't see it as an option."
In December, Lanning started training to care for Damien.
Damien's only concern about living with his teacher?
He was worried he might have to do a lot of homework, the math instructor told CNN with laughter.
But Lanning said math is a subject Damien does well in.
"I'll be his teacher for another year before he's off to high school," he said.
The two share a love of food and enjoy cooking together, but with his kidney problems, the boy can't eat a lot of their creations.
"His favorite thing to cook is seafood," Lanning said. "Hopefully soon he will be able to eat things."
Damien looks forward to eating nachos from 7-Eleven.
"It's always been a favorite," the boy said. "And I want a hot and spicy chicken sandwich from McDonald's with extra mayonnaise."
Lanning and Damien are adjusting to their new lives together after more than three months.
Because of the boy's dietary restrictions, their food bill is high. "We spend about $200 a week on (groceries)," the teacher told CNN.
Lanning has started a GoFundMe account to help with basic needs.
"It is more expensive than I anticipated to entertain a 13-year-old," he said.
Lanning takes off work twice a week to take Damien to doctor appointments.
"A number of teachers have donated their vacation time off. The support from my school community has been wonderful," he said. "It can be isolating. It makes us not feel so alone in the process. It's huge."
Lanning said he is determined not to let Damien down. He said his priorities are to provide stability and help get the boy a kidney. Down the line, he said he hopes to adopt Damien.