Lesson preparation, marking and administration keep the Hong Kong-based maths and science teacher at work for up to 10 hours a day, making the island one of the worst places in the world to teach.
And he spends at least another two hours a day preparing for the next day's teaching.
Mr Wong said reforms bringing in school-based management, targets and in-service training in teachers' own time, had increased workload and taken a heavy toll.
He has been in teaching for nearly 20 years and works in a low-band school - for low-achievers - with up to 42 students in a class.
He blames the poor performance of his pupils on the island's inflexible and old-fashioned education system. "Most of our pupils have psychological problems. We work like robots. I teach, they listen. I write on the board, they copy," said Mr Wong.
He teaches years 7 to 11 - aged 12 to 17 - and knows that less than 5 per cent are likely to gain the necessary points in their Hong Kong Certificate of Education Examination (the equivalent of GCSE) to proceed to A-level.
His major concern, he said, was to ensure his students would not be a risk to society.
Marking remains the greatest burden. The tally for Mr Wong, by no means unusual for the island's teachers, is about 400 exercise books a week, which take at least three hours a day.
The reforms, he believes, have brought only trouble to teachers and school.
"They measure our work according to numbers and percentages, not by what is really happening. It is not about the quality of what our students are learning, just results."