"The schools had become market-driven," says Chan.

"In the early 2000s, because … there were not enough pupils to occupy all the schools, the government said this was a waste of resources. So schools that could not attract enough pupils were forced to shut down."

The problem was exacerbated by a government policy that required schools to be accredited, he adds. "If you were not well accredited, parents would not choose your school."

As a result, Chan says, principals and teachers became obsessed with recruiting enough pupils to stay afloat - to the detriment of their teaching quality.

"So they pushed pupils to get good results in their exams to attract the parents. But teachers … focused on those who could get better results and had no time to take care of those who couldn't keep up," he says.

Chan also saw many well-to-do parents hire private tutors to help their children cope with their schools' heavy focus on exams. But children from families too poor to afford extra help tended to fall behind their peers, disengage from their studies, and eventually drop out of school.

This did not gel with his values as an educator. "Education, to me, is what minimises the gaps in society," he says.

So in 2009, Chan quit his role as principal of QualiEd College to pursue his vision.

He decided to start an organisation - the Equal Opportunities Education Fund - to give every child in Hong Kong a chance to receive a good education, no matter their circumstances.

At the time, he was already volunteering regularly at a centre for disadvantaged children in Kowloon. He tested his idea for a free private tutoring service by asking around in the centre, and many of the children said they would use it. "It takes some time for them to trust the teachers, but deep in their hearts, they are willing to learn," he says.

In the early years of starting up the fund, Chan's fundraising efforts were often met with scorn.

"When I talked to potential donors, many would say 'For kids who drop out, it's their own fault, they're just lazy. It's not society's responsibility'. But now they understand," he says.

Today, the fund has more than 2,000 registered pupils, from preschool to secondary school. Working with just two full-time staff, Chan facilitates one-on-one sessions between pupils from disadvantaged backgrounds and volunteer tutors.

Most of the tutoring is one-on-one in a public location near the students' homes - often in McDonald's or a public library.

The tutors are a mix of university students, retirees and people with full-time jobs. But Chan will not accept teachers, because "I want them to focus on their own students", he says.

In Chan's ideal world, there would be no need for services like his. Each teacher would have the time and interest to address each pupil's individual needs.

But the Hong Kong school system still has a long way to go, he says.

Has there been any improvement in the way schools are being run in recent years? "I don't see it," says Chan, although he admits there have been improvements in society.

"We have changed some mindsets in the community. More and more people now know about the needs of disadvantaged students," he says.

When he quit a prestigious job as a school principal four years ago, Chan forwent a triple-digit monthly salary to run a grassroots charity organisation.

His family of five now relies on the salary of his wife, a civil servant, as well as a modest income Chan receives from writing columns for local newspapers and magazines. "It's not a big sacrifice. I was poor when I first came to Hong Kong and I still had a happy life. I know you don't need money to be happy", he says.

As a principal, Chan was trapped in a system he could not change. But these days, he derives joy and satisfaction from his work. His pride is obvious as he announces that one of his first pupils starts university this year.