Eleven-year-old Christopher Nell was first diagnosed with leukemia when he was three, after his mum noticed bruises on his legs and her son having lots of naps.

He's had three relapses of the disease and two transplants of umbilical cord blood and is currently in remission.

Christopher's mum, Cathy, says he's lost his hair through chemotherapy more times than she can count. She keeps ''umpteen little plastic bags'' containing his fallen hair and bearing the date of his treatment.

Christopher's classmate in grade 5 at Kaleen Primary School, Elijah Arranz, has had his hair cut short only once in his 10 years. But the schoolboy is prepared to shave off his long, lustrous locks in honour of Christopher after raising more than $5000 for the World's Greatest Shave fundraiser for the Leukemia Foundation.

Christopher has some sage advice for his friend ahead of a Canberra winter: ''Make sure you have plenty of beanies and hats.''

While his long, thick hair has been part of his make-up for so long - including bouncing around while he's on the basketball court - Elijah nevertheless told his mother Robin that he ''wanted to shave my head off for Chris''.

''I will obviously miss the hair dramatically, but I'm very excited for him and very proud of him,'' Mrs Arranz said. Both boys also have red hair, with Mrs Arranz saying it's a case of ''fellow rangas unite''.

Elijah says he wanted to be part of the World's Greatest Shave because ''the money raised can buy medical treatments for sick kids and help testing for people who catch leukemia''. Christopher gently pointed out, ''technically Elijah, leukemia isn't contagious''.

Elijah was ''very excited'' about having his hair shaved at a school assembly today. Christopher reckons he will keep a bit of his mate's hair to ''make a Padawan braid'' - fans of Star Wars will know that refers to a member of the Jedi order. Of course.

''Yes, mum wants to keep some of my ponytail too,'' Elijah said.

Mrs Nell said Christopher's latest relapse in 2009 saw the leukemia affect his bone marrow and central nervous system. His illness meant he had to start school a year later than he would have otherwise and also miss out on all of grade 3.

''He's quite a quiet child, because he's not had … the option to do sport and other physical things. But he's really a happy kid. He loves his Lego and his computer games and his Star Wars,'' she said.

The school had been a great support to herself and husband Tim and Elijah's efforts were touching.

''You can understand adults who would volunteer to do that, because maybe intellectually they have a handle of the issues. But for Elijah to be motivated to do that, I think it's quite spectacular,'' Mrs Nell said.

To donate to Elijah's World's Greatest Shave effort, go to my.leukaemiafoundation.org.au/Elijah.