Sister Linda Sim always dreamed of helping other people through taekwondo. The nun, a black-belt in the martial art, gave up taekwondo to join the Franciscan Missionaries of the Divine Motherhood convent in England — on the other side of the world from her home country of Singapore. Now, Sim has returned to Singapore — and she’s teaching taekwondo to children battling childhood cancers.

Sim spent 17 years in England and three more in Africa before her return to Singapore in 2004. She returned to take care of her mother, who was diagnosed with Alzheimer’s disease. Upon her arrival, Sim noticed the Singapore Taekwondo Federation had partnered up with Mount Alvernia Hospital to teach childhood cancer patients the sport.

The kids were "stuck inside playing snakes and ladders” said Ming Wong, secretary general of the Federation to the BBC. The Federation agreed to provide training classes for the patients who could benefit from the sport. Sim was immediately drawn to the cause and offered to teach a weekly class

"That was what I had to leave behind in order to be a sister, and so I thought ‘now I'm reunited,’” Sim told the BBC. The taekwondo-teaching nun now holds a weekly class for about 20 people — all of whom have brain tumors or childhood leukemia. Many of Sim’s students have been trained under her supervision for years — three of her students are now in their 20s.

Ng Wei Hau, one of the nun’s older students, was diagnosed with a brain tumor at the age of 12. Hau was originally told by doctors he had just six months to live, but now the 23-year-old walks without the assistance of a wheelchair or cane.

“When I first met him he was in a wheelchair. When he reached 21 he was walking with a frame, when he reached 23 he had a stick, and now he walks unaided," said Sim. Despite being partially deaf and blind, Hau earned a black belt in taekwondo last year under the Sim’s direction.

Although most nuns teach catechism classes to children, Sim believes she is able to spread the values and benefits of religion through the teaching of taekwondo without quoting scripture. "It gives me a lot of peace and satisfaction,” she said. “It's about evangelizing without having to mention going to church.”

Currently, leukemia and cancers of the brain and central nervous system account for more than half of the new childhood cancer cases, according to the National Cancer Institute. The causes of childhood cancers remain largely unknown. While diagnoses are on the rise, death rates have dramatically decreased in recent years, with five-year survival rates increasing for most of the cancers. Ongoing investigations aim to examine the causes of and the most effective treatments for common childhood cancers.