It is not realistic to make Putonghua compulsory for teachers and students in Hong Kong. As Hong Kong has been a colony of British, most people in Hong Kong are native English or Cantonese speakers. They are not familiar to Putonghua.
In 1980s, Putonghua was not a compulsory subject for students. At that time, Putonghua was not important at all. In early 1990s, Putonghua has been made compulsory for all students, in order to prepare for the return of Hong Kong to China. This policy has been adopted for about 10 years only. Most of the teachers nowadays may not have enough knowledge in speaking Putonghua, They don't really have the ability to teach in Putonghua. Although they can have training courses, it's a bit too late. Of course the Government may employ native Putonghua teachers from China, then what is the use of most of the Hong Kong teachers? They should be fired, shouldn't they? This is not a long term way.
Most Hong Kong students are native Cantonese speakers. They have the privilege of learning in their native tongue. With teaching them in their mother language, they can understand and absorb knowledge easily. They may find fun in learning and willing to go to school. We shouldn't force them to learn in a strange language, this will probably reduce their interest.
Although Putonghua is the most popular language of the world, it's just because China has the highest population, it's nothing to do with its importance. As we all know that English is an international language, it is much more important than Putonghua. Nowadays China has been made to be internationalized by joining the World Trade Organization. China people should learn better English, in order to go with the world. In fact, every...