Lachie's family became involved with CanTeen when his older sister Abi was diagnosed with neuroblastoma at birth.
Abi's tumour was wrapped around her spinal cord. The Huddlestons had helped organise the Megawalk for the past four years but this was the first year Lachie planned to walk it.
The 16-year-old, who will tackle the 28km route, said he "always wanted to just get behind the Megawalk and this year had the opportunity to do it".
Lachie added that the peer support network CanTeen provided was "like no other".
"I was surrounded by people who understood my journey and were given a chance to live normally, something that no other organisation offers."
Mitre 10 marketing manager Kerry Meehan said it was great the schools had backed the cause.
"Because CanTeen is supporting teenagers it's a really good way to show their support for their peers," she said.
Lachie started the school campaign.
Woodford House head girl Sophie Foss said "it would be nice to beat the boys".
She said each Woodford student was donating at least $20, "but we're just trying to get as much involvement as possible".
All of the funds raised from the walk go straight to CanTeen Hawke's Bay.
With sunny skies and a high of 21C expected for Sunday, the school that wins will enjoy entry to the Mitre 10 Mega VIP tent with food and cold drinks.
Lindisfarne is also making a trophy for the top school.
Lachie said the money raised between the schools will "ensure the organisation continues to support, develop and empower Hawke's Bay teens living with cancer".
Mitre 10 Megawalk
* The Mega is a 28km run or walk that starts at Mitre 10 Mega, Hastings, at 7.30am.
* The Hafele Half Mega is a 15km run or walk that starts at Awatoto at 9am.
* The Dunlop Short Mega is a 6.5km version which starts behind Ocean Spa on Marine Parade at 10am.
* The Hits Mega Meander is a 3.5km walk or meander starting at 10am at Perfume Point, Ahuriri.
* All routes end at Mitre 10 Mega.
* Admission: Adults (16+) $20, Senior (65+) and Children (5-15) $10, Under-5s free, Family (2 adults & 2 children under-16) $40, Teams of 4 $60
* Nimons buses are available for transport.