Before taking the reins at DBS in 2000, Chang headed three secondary schools - Po Leung Kuk 83 Directors' College, Po Leung Kuk Tang Yuk Tien College and Jockey Club Ti-I College - all of which he set up. And for Chang, there's never been a greater challenge than starting a school from scratch.

"You are involved in everything from buying furniture to hiring teaching staff," he says. "It was a trailblazing move 22 years ago to set up the Jockey Club Ti-I College. The college specialises in training arts and sports students, and there were no specialist schools nurturing specific talents then."

A literature graduate from the University of Hong Kong, Chang joined the Labour Department after finishing his degree, but lasted just one month. The bureaucracy proved too frustrating. Teaching (his subjects were English and economics) was more to his taste. "Teaching provides more freedom," he says.

Of his decades working in secondary schools, Chang says his 12 years as DBS principal involved the most controversy. That is, perhaps, not surprising as he initiated a series of actions dismantling long-held school traditions, which provoked heated objections from students and teachers.

First, he started a practice of visiting classrooms to observe lessons, drawing complaints from teachers that it added to their stress. He also included students' homework and test scores in their year-end assessment.

When a student council was set up, he gave each student a vote so they could elect the members, antagonising prefects who feared the new student body would diminish their power.

But Chang's measures presaged government initiatives in schools.

"Whenever something new is introduced, there are bound to be objections," he says. "After I started observing teachers' lessons, the government launched a comprehensive review of teachers' performance. Including students' routine test marks for annual assessment was a precursor to the launch of school-based assessment [in 2005]."

What most angered students, teachers and DBS alumni was his decision, in 2003, to sign the school up for the Direct Subsidy Scheme. This allows participating schools to set their own tuition fees and offer alternative curricula. But alumni felt this would be a betrayal of the school's mission to help the poor (DBS was established in 1869 as an orphanage for boys) because the higher fees would preclude underprivileged students from entering the elite institution.

For Chang, it was a way for DBS to offer an alternative curriculum, the International Baccalaureate, alongside the local curriculum - and reduce the erosion of students.

"Quite a few of our students leave midway through their schooling to study overseas. [Having] IB can help us retain a portion of them," he says. "The provision of education should involve alternatives."

It has been a costly proposition. About 200 DBS students take the Hong Kong Diploma of Secondary Education exams compared with 60 in the IB programme, and the school has lost HK$10 million running the programme since introducing it in 2009.

Even so, Chang reckons it is a worthwhile move. "I particularly like the IB component called theory of knowledge. The aim is to nurture critical thinking and inquisitive learning by making students analyse questions."

Last year, DBS also became embroiled in controversy when the Audit Commission uncovered a series of financial irregularities at DSS schools. DBS's primary division came under fire for making grossly inaccurate financial forecasts when applying to raise its fees. The school predicted it would have HK$20 million in accumulated operating reserves at the end of 2008-2009, but wound up with HK$81 million.

However, Chang argues a DSS school needs large reserves to maintain smooth operations. "The government didn't give us a cent for the construction of the new buildings, such as the IB complex and music hall, that were part of the campus expansion. We need money for their maintenance."

He adds: "When the government launched the direct subsidy scheme [in 1991], schools enjoyed a lot freedom. Although there are recalcitrants, [DSS] schools should not be placed under a lot of restrictions [as in public schools] as long as they maintain financial transparency and produce clear financial reports."

An outspoken critic of the government, Chang describes its introduction of liberal studies as a new subject under reforms to the senior secondary curriculum as a "ham-fisted" attempt at copying IB's emphasis on critical thinking.

"Liberal studies should not be studied as a subject for public exams. Under IB, students' performance in theory of knowledge is not counted towards their overall marks. If students fulfil all requirements for liberal studies, they should just get a pass instead of the various grades as is the case now.

"The subject should promote self-exploration instead of being exam-oriented. [As a result] the market is now filled with exam tip guides and drills with model answers for liberal studies. The approach is not right as there are no appropriate answers for the subject."

Wading into the roiling national education controversy, Chang says the government has bungled a well-intentioned venture.

"There's nothing wrong in learning about one's own country and history. But there should not be fixed or suggested answers for national education. Instead of singing the praises of the motherland, the curriculum should present students with all the facts so they can form their own views.

"The intention of launching the subject is good. But once it gets off to a wrong start, no matter what you do later, people will just see it as damage control."

Chang's parents' liberal approach to education greatly influenced his own. A former Kuomintang army officer, Chang senior brought his wife and seven children to Hong Kong after the communists seized power in 1949. He eventually became the principal of a primary school in Ta Kwu Ling in the New Territories that his son also attended, before going to DBS. But there was never any pressure on the young Terence to top his class.

It was a more freewheeling atmosphere, Chang says, lamenting the pressure-cooker environment that students must contend with now. "I'd never heard of tutorials when I studied at DBS. Now, portfolios for school admission run to dozens of pages. My own résumé is just two to three pages long."

Chang has seen his share of monster and helicopter parents over the past four decades, noting how a number go to extremes to ensure their children shine at school or to protect them from any kind of hurt.

He recalls, for instance, a couple who offered HK$10 million to install an escalator so that their child would not have to trudge up a flight of stairs (170 steps) to class.

"Parents should take it easy," he says, adding that being overly protective of offspring and refusing to tolerate the slightest setbacks in class or scrapes on the sports field is not good for their development.

In a wry farewell to his colleagues in education, Chang staged two nights of stand-up comedy at Kitec hall in July, sending up Hong Kong's quirks in schooling and raising children.

During his time at DBS, Chang has encouraged risk-taking as a part of students' education. Every year, he allocated part of the school's funds towards student projects, giving them a chance to flex their business and creative muscles. Capped at HK$50,000 for each project, the applications included publishing a book on students' struggles in the exam system and running stalls at the annual Lunar New Year fair in Victoria Park.

"Even though the projects lost money, they were valuable learning experiences," he says.

One of the more creative ideas came in just before Chang left the school: three students hoped to get funding to shoot a horror movie at the school's sprawling campus in Mong Kok. "They wanted to follow in the footsteps of our famous alumnus Alex Law Kai-yui [director of which won a Crystal Bear at the 2010 Berlin International Film Festival]," he says.

Chang practices what he preaches. Like his father before him, he left his son largely to his own devices at school. "I just let my son do whatever he wanted," he says. "If I were more anxious about his academic results like local parents, he might be more successful. But what he has accomplished so far [teaching architecture at Polytechnic University] is not bad."