Katie Jessop made the decision in August last year to grow her hair as long as she could to make a wig for a child suffering from cancer or alopecia.
The 11-year-old already had "pretty long" hair last year, and said she was just going to go to the hairdressers to have it shortened.
Katie's mother Tammy Jessop did some research and came across Variety SA's hair with heart program.
"Mum suggested to donate it...it's better than throwing it in the bin if it goes to another little girl," said Katie.
She said if she was the girl getting the wig, she wouldn't know how to react.
"I wouldn't really say anything, I'd be speechless," she said.
Katie said she needs a minimum of 35.5 centimetres of hair to donate, which will be measured out carefully on the day and cut by a hairdresser in front of her fellow students at the Port Lincoln Primary School assembly next Friday.
She said her classmates were excited, and Variety balloons and stickers were also organised for the event.
She also said she doesn't mind having short hair, and actually likes the idea of it after having grown her hair for so long.
Chief executive officer at Variety SA David Sexton said people like Katie make a big difference for Aussie kids.
"We can't thank people like Katie enough for their dedicated efforts to help us help Aussie kids," he said.
"Variety doesn't receive any government funding so every wig and every piece of equipment granted to families is thanks to the amazing efforts of people like Katie."
Katie is also fundraising money along with her hair donation, as she said wigs can about $2000 each, and young children need new ones every couple of years.
Her goal is to reach $1500, with the school to host a casual clothes day to help fundraise.
To donate, visit hairwithheart.everydayhero.com/au/katie-s-hair-cut-for-variety.