As well as the wigs and mufti, there will also be sausage sizzle and jolly jar fundraising at the school.
Joshua was diagnosed with leukaemia when he was 2. He had treatment for three-and-a-half years and has been in remission for nearly two years.
"He's good, but he still has lots of days off [school] because his immune system's low," said mum Cathy.
He has more than 700 Beads of Courage representing the different procedures he has been through, including chemotherapy, days spent in isolation, injections, overnight hospital stays and scans.
At the Child Cancer Foundation street appeal in March he helped collectors raise $300 at Te Puke New World.
Now in its fourth year, Wig Wednesday will take place on June 19.
More than 400 schools, businesses and organisations nationwide have signed up for the event, which promises to be a fun fundraising day with a difference.
The foundation's business development manager Claire Robb said people could join in on the fun simply by registering on the foundation's website, wearing a wig on the day and making a donation.
"People really got into the spirit of the event last year by wearing some incredible wigs.
"Importantly, over $100 000 was raised so we're hoping this year will be just as successful."
Three Kiwi kids are diagnosed with cancer every week in New Zealand. The Child Cancer Foundation supports children diagnosed with cancer and their families without any government funding.
