Yu Maoyuan comes from Guizhou province in Southwest China. The 4-year-old was diagnosed with leukemia two months ago and was referred to doctors in Beijing "for better treatment".

On March 18, she attended the class for the first time. The lesson showed how to make a "telephone" with string and two paper cups. Teacher Liu Weixiong used the simple experiment to explain the movement of sound waves to the children.

At first, Yu was timid. She lowered her head and leaned on her mother. She did not say anything, but followed the teachers' instructions.

"She didn't want to go, so I took her to the class," said Yu's mother, who was encouraged by the student volunteers. "My daughter hasn't gone to kindergarten for a long time."

The illness has changed Yu. The course of chemotherapy killed off her cancer cells but weakened her. Her mother said Yu was once an active girl, who loved singing and dancing, but now she is quiet. "She seems upset, but doesn't want to tell us," she said.

Yu completed the paper cup telephone in 30 minutes. When she was asked to test it, she raised the cup and said, "Mom, I love you."

Everybody cheered. Yu laughed and repeated the phrase, but louder. Her mother, on the verge of tears, said it was the happiest day she had known since Yu first went to the hospital.

In the ward, happy times are brief, and pain can strike at any time.