Teacher Choi Ping-kwan knows what it is like to be the bad boy in school. Today, however, he is helping low academic achievers and law breakers who have been excluded from the standard school system. 'I was a troublemaker and truant in school so I understand them well,' said Mr Choi, who teaches mathematics and physical education at one of seven special schools for maladjusted and socially deprived children. 'I was expelled from St John's Co-educational College in Form 4 for low conduct marks but my mother begged the headmaster for mercy and he allowed me to stay. 'I am a problem teacher teaching problem students,' he said. Mr Choi had problems with students in his first year at his current school - which cannot be named for privacy reasons - but overcame this by making friends with them 'under unusual situations'. 'I think playing basketball or badminton are good ways of making friends. We can co-operate in the playground and have refreshments after games.' Off the sports field, Mr Choi takes students to karaoke events and barbecues two or three times a month, and occasionally pays the bill. 'Through these activities, I can talk to them freely and teach them some skills.' Mr Choi encourages his students to take part in sport competitions with ordinary school students, as he believes it can help them develop positive attitudes about themselves. His school has had concerns about allowing its students to interact this way. However, Mr Choi convinced school officials that it was worthwhile - and the fact that the students did not cause problems under his supervision proved that their trust was not misplaced. In class, he has introduced some innovative teaching methods to stimulate students' interest in learning. For example, he throws dice to teach about probability. 'I seldom repeat what the book says. I tell them my personal experience and I tell them jokes,' said Mr Choi, adding that students liked the humorous approach. With his help, half of his students have been able to progress into ordinary schools. Much to Mr Choi's joy, a former student has returned to teach at the same school. 'I never imagined having a former student as a colleague.' Mr Choi asks each student to evaluate his teaching at the end of each semester. 'They are even asking me to be stricter with them,' he said. 'I happily took up their suggestions.' Since starting a webpage in 2001, he has chatted with many students seeking help, some of whom are strangers to him. Mr Choi's personal time is often interrupted by late-night telephone calls from his students, but he does not mind. 'They talk to me when they feel lonely. I'm glad that I can be of some help.'