Almost 30 T-shirts had already been sold this week.
Most of these had been to other students at the school and their parents.
"Two parents this morning bought them as Christmas presents."
Mr Brock said he had "sweet talked" Fraser Cover Warehouse into selling him T-shirts in bulk at a discounted rate which meant the children could sell the printed shirts at a good price and still make a reasonable profit.
The children's T-shirts are $8 and the adults' are $12.
The children designed the prints themselves and took to the internet to find images to turn into stencils.
Greenpark's art suite was commandeered by the children and used to print the T-shirts.
"We made them distinctly Kiwiana. We can maybe even send some of them to Cambodia for the children."
To make the T-shirts, Mr Brock said Greenpark lent the students $200 to buy the first batch.
"We bought 80 T-shirts and started selling them this week. We've already paid the school back and have another $200 to buy the next lot so we can keep going. It's a little business really.
"The students aren't going to forget this, it's real-life learning experiences."
Mr Brock said the students were planning to set up a stall at one of the weekend markets in October or November to sell the T-shirts.
They had done so well already that Mr Brock said he was considering starting up a website and making T-shirts to order.
"That will then become a business site for the kids to run."
At the end of the year, Denise Arnold will come and talk to the students about what things are needed, then the children will decide how to spend the money they earn.