Last month the boys launched their design company, freetecboards, to make longboards - longer types of skateboards - to cater to the small but booming number of longboard enthusiasts in Hong Kong.
"The company is by boarders, for boarders," says Harry.
"It's not about being successful, or about reproducing the same board over and over again. We want to understand our customers, and also know why they want something. And to do that, you have to be using the same products as them."
They thought of the idea to create their own boards last December after Harry's board snapped in half during a practice. Ordering a new longboard from the United States, the sport's home base, would have cost too much money so Harry turned to his father, Paul, a design and technology teacher. Could he fix it? His father's answer was "Yes".
"So far, it's been a family collaboration," Paul Clarke says. "Harry comes up with the designs, I help the boys make the boards. They then test it out, and his little sister and mum work on the graphics."
Harry's new venture has taught him valuable lessons.
"I've learned a lot of things about creating a company," he says. "For example, I know that things take time - you have to be very patient to do it."
Freetecboards currently offers three designs, including one called "Tommy", the two young entrepreneurs' own design, which costs from US$188.
"It's designed to be faster," Harry says. "A lot of what we manufacture is feedback-based. We listen to everything, from e-mails to the official Facebook page."
Harry began riding longboards after he was inspired by his friends, who had already taken up the sport. They live in the Sai Kung area.
Pierre and Harry say that Stanley Plaza and the Sai Kung Waterfront are among Hong Kong's best places for longboarding.
"It's not about the tricks," Pierre says. "The feeling you get when you clear a hill - it's absolutely indescribable."
Harry agrees. "It's really about enjoying your surroundings and breathing it all in - just cruise and enjoy the ride."