For Robin Cheung Man-biu, the classroom and even the principal's office was never enough.
He is one of those people who always wants to do more for education. He built Tsung Tsin College in Tuen Mun, was an active member of policy bodies such as the University Grants Committee and Advisory Committee on Teacher Education and Qualifications, and has been a prolific writer in the media.
After retiring from his role as a principal, he embarked on a second career as a part-time lecturer at Chinese University of Hong Kong, where he teaches about effective school leadership and leading change.
He is also a co-founder of the year-old Principals' Institute and a school manager, keeping his ear to the ground on the latest developments in education.
As a prominent voice among principals past and present, he has now shared his insights in a collection of his writings in English and Chinese: 40 Years a Teacher: A Life in Learning. His purpose, he says, is to deepen the discourse on the education issues facing Hong Kong.
The learning in the title of his book refers as much to his own development as that of his students. Cheung, after all, worked his way up from being a non-graduate teacher to one of the few principals to have spent their spare time completing a doctoral degree.
He puts his motivation to strive for better roles down to his "big ego". But that is a self-deprecating assessment by this deeply Christian, humble yet very determined man.
At school level, a theme that runs through his career and his book is how to "restart the engine" of less motivated students and to give equal opportunities to those from disadvantaged backgrounds.
He recently developed a "learning motivation strategies toolkit" for this purpose and used the Healthy Schools Award Scheme as a platform to link individual and community health to improved learning in his school.
His essays from the 1990s call for students' interests to be placed at the centre of all educational planning and change. The reform programme developed by the Education Commission and rolled out since has had that purpose.
Yet his more recent writings in the book suggest that many of the limitations and pressures of the system that he complained about in the past remain.
They are exacerbated by competition for university places and increasing competition between and within schools. Furthermore, he sees a growing equality gap between children in better-funded elite Direct Subsidy Scheme schools and those in the aided and government sectors.
"The superficial part of the reforms to the academic structure are now in place and running smoothly: new subjects, new exams, a new assessment scheme," he says.
This allows students to have more space to learn and to choose subjects they like. It also introduced liberal studies as a core subject to help students develop different perspectives on various topics.
"I would not say there is no change at all," he says. "We have the form but I am asking: 'Do we have the substance or spirit yet?'
"Students are so focused on their academic performance and university admission they don't care about anything outside the exam syllabus and exam skills."
And as competing schools favour those students who can boast the best grades and highest chance of going to university, exams are what teachers are focusing on.
"It means that after so much fuss about changes in teaching and learning advocated by the education reform, nothing really happens."
Cheung talks of the need for a new culture to produce leadership among principals and "space" for teachers to try new things. But this is also a book about the motivation for being a teacher.
In 2006, Cheung told graduating students of the Hong Kong Institute of Education: "You need to put the heart back into teaching and pastoral care.
"Teaching is more than the mere passing of cold knowledge and skills to students. It also involves the passionate fostering of values, the enthusiastic modelling of learning, and the unapologetic manifestation of love and care for students."
He urged the graduates to be caring, ethical, reflective and daring.
Cheung is a brilliant role model for young educators.
This book's greatest value will be in inspiring the next generation to share the passion he has had for his profession and the difference it can make for young people.
40 Years A Teacher, A Life in Learning is published by Trinity Culture Limited.Katherine Forestier is director of the consultancy Education Link